Method and systems for measuring neural activity

ABSTRACT

Provided herein is a method of optically recording neural activity in one or more regions of a target tissue. Also provided is a method of optically modulating the activity of a neural tissue. Further provided is a system that finds use in performing the present methods.

CROSS-REFERENCE

This application is a continuation of U.S. application Ser. No.15/749,052, which is a U.S. National Phase application under 35 U.S.C. §371 of PCT Application No. PCT/US2016/062314, filed Nov. 16, 2016, whichclaims the benefit of U.S. Provisional Patent Application No.62/257,140, filed Nov. 18, 2015, which applications are incorporatedherein by reference in their entirety.

INTRODUCTION

Genetically-encoded Ca²⁺ indicators (GECIs) are polypeptides whosefluorescence is modulated by intracellular concentration of calciumions. GECIs are used to optically measure neuronal activity at singleresolution and to study in vivo dynamics and population coding under amicroscope system.

Optogenetic refers to methods of manipulating the activity of excitablecells, such as neurons, by altering the membrane potential of excitablecells expressing light-activated proteins that depolarize orhyperpolarize cells in response to light.

Optical fibers, which bi-directionally transmit light between separatesites, can be used for optical imaging and/or manipulating neuralactivity relevant to behavioral circuitry mechanisms.

SUMMARY

Provided herein is a method including a) illuminating one or moreregions of a target tissue with a light stimulus comprising light pulsesof a plurality of wavelengths, wherein each of the one or more regionscomprises one or more collections of a plurality of neurons, or asubcellular portion thereof, labeled with one or more neuralactivity-dependent fluorescent moieties; the light pulses comprise: i) afirst set of light pulses at a first wavelength; and ii) a second setlight pulses at one or more wavelengths, wherein each of the one or morewavelengths are different from the first wavelength and are at anexcitation wavelength of the one or more neural activity-dependentfluorescent moieties, and wherein each light pulse of the first set areinterleaved among light pulses of the second set, thereby generatingfluorescence from each of the one or more regions, wherein a multimodeoptical fiber is configured to direct the light stimulus to, and collectthe fluorescence from, each of the one or more regions; b) recording,onto independent frames of an image detector for each light pulse, animage of a cross-section of the multimode optical fiber for each of theone or more regions, wherein a cross-sectional average of thefluorescence generated in response to the second set of light pulses isrepresentative of an aggregate neural activity of the one or moreregions; and c) analyzing the recorded image, to generate an outputcomprising a measure of the aggregate neural activity in each of the oneor more regions. In some embodiments, the multimode optical fiber has adiameter in the range of 100 to 1000 μm. In some embodiments, the one ormore collections include one or more functionally-defined collections ofa plurality of neurons.

In any embodiment, the one or more regions may include: a firstcollection of a plurality of neurons, each neuron of the firstcollection containing a first neural activity-dependent fluorescentmoiety; and a second collection of a plurality of neurons, each neuronof the second collection containing a second neural activity-dependentfluorescent moiety, and wherein the second set of light pulses include:a third set of light pulses at a second wavelength, different from thefirst wavelength, wherein the second wavelength is at an excitationwavelength of the first neural activity-dependent fluorescent moiety;and a fourth set of light pulses at a third wavelength, different fromthe first and second wavelengths, wherein the third wavelength is at anexcitation wavelength of the second neural activity-dependentfluorescent moiety, and wherein the recording includes recording a firstimage and a second image of the terminal cross-section of the multimodeoptical fiber from each of the one or more regions, wherein across-sectional average of the fluorescence generated in response to thethird set of light pulses in the first image is representative of anaggregate neural activity of the first collection of a plurality ofneurons, and a cross-sectional average of the fluorescence generated inresponse to the fourth set of light pulses in the second image isrepresentative of an aggregate neural activity of the second collectionof a plurality of neurons. In some cases, the first collection and thesecond collection are distinct collections of a plurality of neurons. Insome cases, the first collection and the second collection arenon-overlapping collections of a plurality of neurons. In someembodiments, the light pulses of the third set and light pulses of thefourth set are synchronous.

In any embodiment, the light stimulus may include an alternating orderof a light pulse from the first set of light pulses and one or morelight pulses from the second set of light pulses.

In any embodiment, the analyzing may include: 1) demarcating thecross-section of the multimode optical fiber from each of the one ormore regions in the recorded image; and 2) calculating an average of thefluorescence across each of the cross-sections.

In any embodiment, the analyzing may include 3) calculating a normalizedchange in the fluorescence over a baseline fluorescence for eachcross-section of the multimode optical fibers in the recorded image. Insome cases, the baseline fluorescence is a median of the averagefluorescence within each cross-section of the multimode optical fibersacross a plurality of recorded images.

In any embodiment, a neural activity-independent fluorescence may begenerated in response to the first set of light pulses. In someembodiments, the first wavelength is at an isosbestic point of at leastone of the one or more neural activity-dependent fluorescent moieties.In some cases, the analyzing includes 4) subtracting an average of theneural activity-independent fluorescence across a cross-section from anaverage of the neural activity-dependent fluorescence across thecross-section, to obtain a motion-corrected measure of the aggregateneural activity.

In any embodiment, at least one of the one or more regions includes athird collection of a plurality of neurons, or a subcellular portionthereof, each neuron of the third collection containing alight-activated polypeptide configured to modulate the electricalactivity of the neuron in response to the light stimulus, wherein thefirst wavelength is at an activation wavelength of the light-activatedpolypeptide. In some embodiments, the third collection comprises afunctionally-defined collection of a plurality of neurons. In somecases, the third collection includes the same neurons as at least one ofthe one or more collections of a plurality of neurons. In someembodiments, the light pulses of the second set have a power of 50 μW orless. In some embodiments, light pulses in the first set are pulsed at afirst frequency less than a second frequency at which light pulses ofthe second set are pulsed. In some embodiments, the light pulses of thefirst set have a power sufficient to approximate neuralactivity-dependent fluorescence generated by a natural stimulus. In someembodiments, the light-activated polypeptide is a depolarizing orhyperpolarizing light-activated polypeptide. In some embodiments, thelight-activated polypeptide is an ion channel or an ion pump. In somecases, the light-activated polypeptide is selected from: ChR2, iC1C2,C1C2, GtACR2, NpHR, eNpHR3.0, C1V1, VChR1, VChR2, SwiChR, Arch, ArchT,KR2, ReaChR, ChiEF, Chronos, ChRGR, CsChrimson, bReaCh-ES, and variantsthereof.

In any embodiment, the target tissue may be an in vivo tissue. In someembodiments, the target tissue is in a freely moving animal.

In any embodiment, the method may include illuminating two or moreregions of the target tissue. In some cases, the two or more regionsinclude functionally distinct regions of the target tissue. In someembodiments, the two or more regions comprise anatomically distinctregions of the target tissue. In some embodiments, the two or moreregions comprise functionally connected regions of the target tissue.

In any embodiment, the one or more regions may include one or moremammalian brain regions. In some cases, the one or more mammalian brainregions is selected from at least a portion of the ventral tegmentalarea (VTA), prefontal cortex (PFC), nucleus accumbens (NAc), amygdala(BLA), substantia nigra, ventral pallidum, globus pallidus, dorsalstriatum, ventral striatum, subthalamic nucleus, hippocampus, dentategyrus, cingulate gyrus, entorhinal cortex, olfactory cortex, sensorycortex, thalamus, primary motor cortex, and cerebellum.

In any embodiment, one or more regions may include neuronal projectionsof the one or more collections of a plurality of neurons. In some cases,the neuronal projections are axonal projections.

In any embodiment, the one or more neural activity-dependent fluorescentmoieties may include a genetically-encoded indicator dye.

In any embodiment, the one or more collections may include a pluralityof dopaminergic, cholinergic, GABAergic, glutamatergic, or peptidergicneurons.

In any embodiment, the one or more neural activity-dependent fluorescentmoieties may include a calcium- and/or a voltage-sensitive indicatordye.

In any embodiment, the one or more collections may include geneticallymodified neurons expressing the one or more activity-dependentfluorescent moieties. In some cases, expression of each of the one ormore neural activity-dependent fluorescent moieties is regulated under acell-specific promoter. In some cases, expression of each of the one ormore neural activity-dependent fluorescent moieties is regulated in aCre-dependent manner. In some embodiments, the method further includes,before the illuminating, genetically modifying neurons of the one ormore regions of the target tissue to express the one or more neuralactivity-dependent fluorescent moieties.

In any embodiment, the image detector may be a charge-coupled device(CCD) or a complementary metal oxide semiconductor (CMOS) camera.

In any embodiment, the recording may include recording the imagesynchronously with the second set of light pulses.

In any embodiment, the recording comprises recording the imagesynchronously with the first set and second set of light pulses.

Also provided herein is a system that includes a) an illumination unit;b) an objective, wherein the objective is configured to receive lightfrom the illumination unit and to focus the light at a working distancefrom the objective; c) a plurality of light conduits, each light conduitcontaining one or more multimode optical fibers and defining a firstend, a second end opposite the first, and a light conduit numericalaperture, wherein a terminus at the first end of each of the lightconduits is at the working distance from the objective; a terminalcross-section of a multimode optical fiber at the first end of each ofthe light conduits is in a field of view of the objective; and the lightconduit numerical aperture is less than a numerical aperture of theobjective; and d) an image detector; wherein the system is configuredto: generate a light stimulus including light pulses of a plurality ofwavelengths; illuminate a region in a target tissue at the second end ofeach of the plurality of light conduits, the region containing one ormore collections of a plurality of neurons, or a subcellular portionthereof, labeled with one or more neural activity-dependent fluorescentmoieties, wherein the plurality of wavelengths comprises one or morewavelengths at an excitation wavelength of the one or more neuralactivity-dependent fluorescent moieties; collect fluorescence from theregion at the second end of the same light conduit of the plurality oflight conduits used to illuminate the region; and record an imageincluding all of the terminal cross-sections of the multimode opticalfibers at the first end of the light conduits onto a frame of the imagedetector. In some embodiments, the one or more multimode optical fibershave a diameter in the range of 100 to 1000 μm. In some embodiments, thenumerical aperture of the multimode optical fiber is 0.30 or greater. Insome embodiments, the second end is configured to be implanted in thetarget tissue.

In any embodiment, each of the light conduits may include: animplantable fiber-optic element including an attachment element; and oneor more multimode optical fibers configured to attach to the attachmentelement.

In any embodiment, the plurality of wavelengths may include a wavelengthat an isosbestic point of the one or more neural activity-dependentfluorescent moieties.

In any embodiment, the plurality of wavelengths may include a pluralityof wavelengths at an excitation wavelength of a plurality of neuralactivity-dependent fluorescent moieties.

In any embodiment, the plurality of wavelengths may include one or morewavelengths at an activation wavelength of one or more light-activatedpolypeptides.

In any embodiment, the light source may be a light-emitting diode (LED)or a laser.

In any embodiment, the image detector may be a charge-coupled device(CCD) or a complementary metal oxide semiconductor (CMOS) camera.

In any embodiment, the system further may include an image splitterpositioned in front of the image detector.

In any embodiment, the system may further include: e) a processor; andf) a computer-readable medium containing instructions that, whenexecuted by the processor, causes the system to: generate a lightstimulus containing i) a first set of light pulses at a firstwavelength; and ii) a second set of light pulses at one or morewavelengths, each of the one or more wavelengths different from thefirst wavelength, using the illumination unit, wherein the one or morewavelengths are each at the excitation wavelength of the one or moreneural activity-dependent fluorescent moieties, and wherein each lightpulse of the first set are interleaved among light pulses of the secondset, thereby generate fluorescence from each of the one or more regions;and record the image onto independent frames of the image detector pereach light pulse. In some cases, the one or more wavelengths include twoor more wavelengths.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1H are a collection of diagrams and graphs showing simultaneouscalcium measurements from multiple deep brain regions using an sCMOScamera, according to embodiments of the present disclosure.

FIGS. 2A-2H are a collection of diagrams and graphs showing dual-colorimaging of different populations and simultaneous recording andperturbation of neural activity according to embodiments of the presentdisclosure.

FIGS. 3A-3C are a collection of diagrams and graphs showing synchronouscamera and photoreceiver measurements of reward-related photometrysignals in the VTA, according to embodiments of the present disclosure.

FIGS. 4A-4F are a collection of images and graphs showing GECIfluorescence emission to calcium-dependent excitation wavelengths and toa calcium-independent isosbestic wavelength, according to embodiments ofthe present disclosure.

FIG. 5 is a collection of graphs showing an example of correctingmotion-related artifacts present in the 410 nm isosbestic wavelength,according to embodiments of the present disclosure.

FIGS. 6A-6C are a collection of graphs showing example traces ofsimultaneous 4-fiber recordings of VTA-DA cell bodies and projectionsduring reward and tail shock, according to embodiments of the presentdisclosure.

FIGS. 7A-7D are a collection of images showing confirmation of fiberlocation and virus expression for 4-fiber surgeries, according toembodiments of the present disclosure.

FIGS. 8A and 8B are a collection of diagrams showing microscopeconfigurations used for dual-color imaging and simultaneous imaging andperturbation experiments, according to embodiments of the presentdisclosure.

FIGS. 9A and 9B are a collection of images showing confirmation of fiberlocation and virus specificity for dual-color imaging, according toembodiments of the present disclosure.

FIGS. 10A-10F are a collection of graphs showing the characterization ofa bReaCh-ES opsin, according to embodiments of the present disclosure.

FIGS. 11A-11D are a collection of graphs showing control experimentalresults for simultaneous imaging and perturbation experiment, accordingto embodiments of the present disclosure.

FIG. 12A-12F provide amino acid sequences of ReaChR and bReachESpolypeptides.

FIG. 13A-13S provide amino acid sequences of single-fluorescent proteingenetically encoded calcium indicators.

FIG. 14A-14C provide amino acid sequences of multi-fluorescent proteingenetically encoded calcium indicators.

FIG. 15A-15U provide amino acid sequences of various light-responsivepolypeptides.

DEFINITIONS

The terms “polypeptide”, “peptide” and “protein” are usedinterchangeably herein to refer to polymers of amino acids of anylength. The polymer may be linear, it may comprise modified amino acids,and it may be interrupted by non-amino acids. The terms also encompassan amino acid polymer that has been modified; for example, disulfidebond formation, glycosylation, lipidation, acetylation, phosphorylation,or any other manipulation, such as conjugation with a labelingcomponent. As used herein the term “amino acid” refers to either naturaland/or unnatural or synthetic amino acids, including glycine and boththe D or L optical isomers, and amino acid analogs and peptidomimetics.

The term “genetic modification” refers to a permanent or transientgenetic change induced in a cell following introduction into the cell ofa heterologous nucleic acid (e.g., a nucleic acid exogenous to thecell). Genetic change (“modification”) can be accomplished byincorporation of the heterologous nucleic acid into the genome of thehost cell, or by transient or stable maintenance of the heterologousnucleic acid as an extrachromosomal element. Where the cell is aeukaryotic cell, a permanent genetic change can be achieved byintroduction of the nucleic acid into the genome of the cell. Suitablemethods of genetic modification include viral infection, transfection,conjugation, protoplast fusion, electroporation, particle guntechnology, calcium phosphate precipitation, direct microinjection, andthe like.

A “plurality” contains at least 2 members. In certain cases, a pluralitymay have at least 10, at least 100, at least 1000, at least 10,000, atleast 100,000, at least 10⁶, at least 10⁷, at least 10⁸ or at least 10⁹or more members.

“Substantially” as used herein, may be applied to modify anyquantitative representation that could permissibly vary withoutresulting in a change in the basic function to which it is related.

“Representative” as used herein, may be used to indicate that avariation in an underlying phenomenon is related to a quantity, e.g., ameasured quantity by an experimentally-defined relationship.

“Cellular electrical activity” as used herein, refers to activity ofcells that are related to changes in the concentration of ionic species(e.g., sodium ions, potassium ions, calcium ions, etc.) within the cell.Electrical activity may include changes in the intracellularconcentration of ions, such as calcium ions caused by, e.g., opening orclosing of ion channels in the plasma membrane, endoplasmic reticulum;activation or inactivation of ion pumps or transporters; etc. Electricalactivity may include changes in membrane potential caused by changes inthe concentration gradient of ionic species across the plasma membrane.Cellular electrical activity may include neural activity, i.e., cellularelectrical activity of a neuron or a collection of neurons.

“Interleaved” as used herein, may be used to describe a relationshipbetween a first event and two second events, where the first eventoccurs in between the two second events, and where the first event doesnot overlap with either of the two second events. In some cases, any twoconsecutive events may occur substantially immediately one afteranother.

A “wavelength” as used herein, may include a band of wavelength valuescentered on a specific wavelength value. The width of the band ofwavelength values may vary and may depend on the desired and/orpractical level of differentiation between different excitation andemission lights used in the present optical method and system.

“Excitation wavelength” as used in reference to a neural-activitydependent fluorescent moiety, refers to the wavelength by which thefluorescent moiety is excited generates an emission that isrepresentative of neural activity. In some cases, the excitationwavelength is the optimal wavelength at which neural-activity dependentfluorescence is emitted by the fluorescent moiety.

“Isosbestic point” as used herein, may refer to a wavelength at whichthe total absorbance (i.e., fluorescence) of a neural-activity dependentfluorescent moiety does not change regardless of theelectrophysiological state of the cellular milieu. Thus, a calciumindicator in a neuron stimulated by light having a wavelengthsubstantially at the isosbestic point of the calcium indicator will emitthe same intensity of fluorescence regardless of the concentration ofcalcium in the neuron, within the physiological range.

“Working distance” as used herein, refers to the distance between thefront edge of the objective lens (e.g. the surface of the front lensclosest to the sample being observed in a typical light microscopesetup) and the surface of the sample being observed (i.e. the surface ofthe cover glass) when the observed sample is in focus. Working distancemay also indicate the location in front of the objective where a samplewould be in focus.

“Terminus” as used in reference to an optical fiber, refers to an endwhere light enters or exits the optical fiber.

“Cross-section” as used in reference to an optical fiber, refers to anarea defined by an intersection between the optical fiber and a planesubstantially perpendicular to the direction of travel of bulk lightthrough the optical fiber.

An “image detector,” as used herein, refers to an optical detectionand/or recording device that measures light intensity across individualpixels of an optical sensor, where the spatial distribution of theindividual pixels corresponds to a spatial distribution of the source ofthe light. Thus, an image detector may simultaneously capture thespatial distribution of light intensities in a light pattern emittedfrom a sample.

“Frame” as used herein, may refer to a single two-dimensional imagecaptured by exposing the image sensor of an image detector to lightcollected onto the image sensor for a desired amount of time.

“Aggregate” as used herein, may be used to indicate a property orcharacteristic of a population without regard to the individualcontributions to the property or characteristic. Thus, an aggregateneural activity may indicate the neural activity of a population ofneurons without providing any underlying information about the activityof any one of the individual neurons in the population, except in thecase where the population is a single neuron.

“Synchronous” as used herein, may be applied to any two or moresequences of events that occur with a temporal pattern that issubstantially the same. Events in the two or more sequences that aresynchronous may start at substantially the same times, may have amidpoint within events that are at substantially the same times, and/orend at substantially the same times. “Simultaneous” may indicate twoevents that are synchronous and substantially coextensive in duration.

Before the present disclosure is further described, it is to beunderstood that the disclosed subject matter is not limited toparticular embodiments described, as such may, of course, vary. It isalso to be understood that the terminology used herein is for thepurpose of describing particular embodiments only, and is not intendedto be limiting, since the scope of the present disclosure will belimited only by the appended claims.

Where a range of values is provided, it is understood that eachintervening value, to the tenth of the unit of the lower limit unlessthe context clearly dictates otherwise, between the upper and lowerlimit of that range and any other stated or intervening value in thatstated range, is encompassed within the disclosed subject matter. Theupper and lower limits of these smaller ranges may independently beincluded in the smaller ranges, and are also encompassed within thedisclosed subject matter, subject to any specifically excluded limit inthe stated range. Where the stated range includes one or both of thelimits, ranges excluding either or both of those included limits arealso included in the disclosed subject matter.

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which the disclosed subject matter belongs. Although anymethods and materials similar or equivalent to those described hereincan also be used in the practice or testing of the disclosed subjectmatter, the preferred methods and materials are now described. Allpublications mentioned herein are incorporated herein by reference todisclose and describe the methods and/or materials in connection withwhich the publications are cited.

It must be noted that as used herein and in the appended claims, thesingular forms “a,” “an,” and “the” include plural referents unless thecontext clearly dictates otherwise. Thus, for example, reference to “animage” includes a plurality of such images and reference to “the regionof a target tissue” includes reference to one or more regions of atarget tissue and equivalents thereof known to those skilled in the art,and so forth. It is further noted that the claims may be drafted toexclude any optional element. As such, this statement is intended toserve as antecedent basis for use of such exclusive terminology as“solely,” “only” and the like in connection with the recitation of claimelements, or use of a “negative” limitation.

It is appreciated that certain features of the disclosed subject matter,which are, for clarity, described in the context of separateembodiments, may also be provided in combination in a single embodiment.Conversely, various features of the disclosed subject matter, which are,for brevity, described in the context of a single embodiment, may alsobe provided separately or in any suitable sub-combination. Allcombinations of the embodiments pertaining to the disclosure arespecifically embraced by the disclosed subject matter and are disclosedherein just as if each and every combination was individually andexplicitly disclosed. In addition, all sub-combinations of the variousembodiments and elements thereof are also specifically embraced by thepresent disclosure and are disclosed herein just as if each and everysuch sub-combination was individually and explicitly disclosed herein.

The publications discussed herein are provided solely for theirdisclosure prior to the filing date of the present application. Nothingherein is to be construed as an admission that the disclosed subjectmatter is not entitled to antedate such publication by virtue of priorinvention. Further, the dates of publication provided may be differentfrom the actual publication dates which may need to be independentlyconfirmed.

DETAILED DESCRIPTION

As summarized above, methods and systems optically recording cellularelectrical activity, e.g., intracellular calcium dynamics, in one ormore regions of a target tissue are provided. The present methods andsystems provide for rapid, simultaneous optical recording of cellularelectrical activity-dependent fluorescence emitted by a collection ofelectrically excitable cells, e.g., neurons, that are labeled with acellular electrical activity-dependent fluorescent moiety in one or moreregions of a target tissue. The simultaneous recording may be scaled toa number of regions within a target tissue, such that the cellularelectrical activity-dependent fluorescence emitted by a collection ofelectrically excitable cells in two or more regions may be recordedsimultaneously. In some embodiments, the present methods and systemsprovide for simultaneous recording of cellular electricalactivity-dependent fluorescence emitted by a plurality of collections ofelectrically excitable cells in a region, using a plurality of cellularelectrical activity-dependent fluorescent moieties. In some embodiments,the present methods and systems provide for optically modulating theelectrical activity of cells that contain a light-activated polypeptidein conjunction with recording electrical activity. Further aspects ofthe present methods and systems are now described in detail.

Systems

A system of the present disclosure may be described with reference tothe accompanying figures. However, it is noted that the figures may showan example of the specific components of an embodiments of the presentsystem, and that other embodiments of the present system is envisionedto be within the scope of this disclosure, by substituting the specificcomponents with equivalent structural and/or equivalent functionalcomponents known in the art.

A system of the present disclosure includes an illumination unit,including one or more light sources, e.g., a light-emitting diode (LED)and/or a laser light source, that may be configured to emit light at asuitable wavelength (FIGS. 1A, 8A and 8B). Having multiple light sourcescan allow the user to control the illumination pattern, e.g., the timingof light pulses, for each light source independently of each other. Theillumination unit may also include any other suitable optical componentsto direct, focus and otherwise control the light being generated by thelight source. Suitable optical components include, but are not limitedto, lenses, tube lenses, collimators, dichroic mirrors, filters,shutters, etc. Thus, the illumination unit may be configured to projecta light stimulus that includes light pulses of a number of wavelengths.A controller may be in communication with the illumination unit so as tocontrol the timing, duration, and/or wavelength of the light pulsegenerated by the illumination unit.

The present system may also include an objective placed in the opticalpath of the system so as to focus light from the illumination unit atthe working distance of the objective. In front of the object, a bundleof optical fibers, e.g., multimode optical fibers, is positioned suchthat the terminal cross-sections of some or all of the optical fibersare focused and in the field of view of the objective (FIG. 1A, topright inset). The numerical aperture of the optical fiber can be lessthan the numerical aperture of the objective. The bundle of opticalfibers may be part of a multi-fiber branching patchcord that terminatesin a number of separate optic fiber branches. The ends of the opticfiber branches may be equipped with a ferrule, e.g., a stainless steelferrule, to allow attachment to optic fibers that are implanted in atissue, e.g., implanted to position the fiber ends in different regionsof a brain in a subject, such as a mouse or rat (see FIGS. 1B, 1F, 2Aand 2E). Thus, the light stimulus generated by the light sources andprojected to the back of the objective through the optical light pathcan be directed into the optical fibers and simultaneously illuminatemultiple, distinct regions of the brain where the branched optic fiberends are implanted.

The same optical fibers used to deliver the light stimulus to the targetregions of a tissue are also configured to collect fluorescence that isemitted from the target areas. Thus, the target regions may contain apopulation of neurons that are genetically modified to express a neuralactivity-dependent fluorescent moiety, such as a genetically encodedcalcium indicator. When a target region is stimulated with a lightstimulus having a wavelength at or around the excitation wavelength ofthe neural activity-dependent fluorescent moiety, the illuminatedneurons may emit fluorescence that is representative of the level ofneural activity in the region. The fluorescence from an individualneuron may be representative of the activity level of the individualneuron. The fluorescence collected from two or more neurons may berepresentative of the average activity level of the neurons. By“average” is meant the arithmetic mean.

The fluorescence emitted from the target tissue and collected by theoptical fibers is directed back to and collected by the objective, andfurther directed to an image sensor of an image detector, e.g. a digitalcamera. The optical path of the collected fluorescence may include anysuitable components, such as a dichroic mirror and lenses, to form animage of the terminal cross-sections of the optical fibers onto theimage sensor and capture the image with the image detector. In somecases, an image splitter may be positioned in the light path before,e.g., in front of, the image detector (FIG. 8A). In such cases, anappropriate configuration of the image splitter can divide thefluorescence emitted from the tissue based on the wavelength andseparate images for different wavelengths of fluorescence may becaptured by the image detector simultaneously.

The light source of a system of the present disclosure may include anysuitable light source. In some cases, the light source is an LED, an LEDarray or a laser. The light source may emit light having a wavelength inthe infrared range, near-infrared range, visible range, and/orultra-violet range. The light source may emit a light at a wavelengtharound 350 nm or more, e.g., around 380 nm or more, around 410 nm ormore, around 440 nm or more, around 470 nm or more, around 500 nm ormore, around 560 nm or more, around 594 nm or more, around 600 nm ormore, around 620 nm or more, around 650 nm or more, around 680 nm ormore, around 700 nm or more, around 750 nm or more, around 800 nm ormore, including around 900 nm or more, and may emit a light at awavelength around 2,000 nm or less, e.g., around 1,500 nm or less, 1,000nm or less, 800 nm or less, 700 nm or less, 650 nm or less, including620 nm or less, or 600 nm or less. In some cases, the light source mayemit a light at a wavelength in the range of about 350 nm to about 2,000nm, e.g., about 410 nm to about 2,000 nm, about 440 nm to about 1,000nm, about 440 nm to about 800 nm, including about 440 nm to about 620nm. The light source may be configured to produce a continuous wave, aquasi-continuous wave, or a pulsed wave light beam. In certainembodiments, a laser light source is a gas laser, solid state laser, adye laser, semiconductor laser (e.g., a diode laser), or a fiber laser.

The number of wavelengths produced by the light source may be anysuitable number of wavelengths. In some cases, the light source produceslight with 1 or more, e.g., 2 or more, 3 or more, including 4 or more,or 5 or more, or 6 or more, or 7 or more, or 8 or more, or 9 or more, or10 or more, distinct wavelengths of light, and produces light with 10 orfewer, e.g., 9 or fewer, 8 or fewer, 7 or less, 6 or fewer, including 5or fewer distinct wavelengths of light. In some embodiments, the lightsource produces light in the range of 1 to 10, e.g., 1 to 8, 2 to 6, 2to 5, including 2 to 4 distinct wavelengths.

The objective may be any suitable objective for use in the presentsystem. The objective may be an air objective, oil objective, waterobjective, a water and air objective, etc. The objective may have anysuitable numerical aperture for use in the present system. In somecases, the objective has a numerical aperture of 0.3 or more, e.g., 0.4or more, 0.5 or more, including 0.6 or more, and has a numericalaperture of 1.6 or less, e.g., 1.4 or less, 1.2 or less, 1.0 or less,0.9 or less, including 0.8 or less. In some cases, the objective has anumerical aperture in the range of 0.3 to 1.6, e.g., 0.3 to 1.4, 0.4 to1.2, 0.5 to 1.0, including 0.5 to 0.9. In some cases, the numericalaperture of the objective is greater than the numerical aperture of anindividual optical fiber that is used to probe a single region in thetissue.

The magnification of the objective may be any suitable magnification,and may be 4× or more, e.g., 10× or more, 20× or more, 40× or more,including 60× or more, and may be 100× or less, 80× or less, 60× orless, including 20× or less. In certain embodiments, the magnificationof the objective may be in the range of 4× to 100×, e.g., 10× to 60×,including 10× to 40×.

Any suitable optical fibers may be used in the present system. Theoptical fiber may be a multimode optical fiber. In some instances, amultimode optical fiber supports more than one propagation mode. Forexample, a multimode optical fiber may be configured to carry a range ofwavelengths of light, where each wavelength of light propagates at adifferent speed.

The optical fiber may include a core defining a core diameter, wherelight from the light source passes through the core. The core may befurther surrounded by a cladding. The core diameter of an individualoptical fiber that is used to probe a single region in the tissue mayvary, and may be any suitable core diameter. In some cases, the corediameter is greater than the wavelength of light carried by the opticalfiber. For example, the core diameter of an optical fiber may be 10 μmor more, e.g., 50 μm or more, 100 μm or more, 200 μm or more, including300 μm or more, and may be 1,000 μm or less, e.g., 900 μm or less, 800μm or less, 700 μm or less, including 600 μm or less. In someembodiments, the core diameter of the individual optical fiber may be inthe range of 10 to 1,000 μm, e.g., 50 to 1,000 μm, 100 to 1,000 μm, 200to 800 μm, including 300 to 600 μm.

In some instances, the cladding surrounds at least a portion of the coreof the optical fiber. For instance, the cladding may surroundsubstantially the entire outer circumferential surface of the opticalfiber. In some cases, the cladding is not present on the ends of theoptical fiber, such as at the end of the optical fiber that receives andtransmits light to and from the illuminating unit, and the opposite endof the optical fiber that receives and transmits light to and from theneurons in the target region of interest in the subject. The claddingmay be any suitable type of cladding. In some cases, the cladding has alower refractive index than the core of the optical fiber. Suitablematerials for the cladding include, but are not limited to, plastic,resin, and the like, and combinations thereof.

In some cases, the optical fiber includes an outer coating. The outercoating may be disposed on the surface of the cladding. The coating maysurround substantially the entire outer circumferential surface of theoptical fiber. In some cases, the coating is not present on the ends ofthe optical fiber, such as at the end of the optical fiber that receivesand transmits light to and from the illuminating unit, and the oppositeend of the optical fiber that receives and transmits light to and fromthe neurons in the target region of interest in the subject. The coatingmay be a biologically compatible coating. A biologically compatiblecoating includes coatings that do not significantly react with tissues,fluids, or other substances present in the subject into which theoptical fiber is inserted. In some cases, a biologically compatiblecoating is composed of a material that is inert (i.e., non-reactive)with respect to the surrounding environment in which the optical fiberis used.

The numerical aperture of an individual optical fiber that is used toprobe a single region in the tissue may vary, and can be less than thenumerical aperture of the objective. Stated another way, the numericalaperture of the objective can be greater than the numerical aperture ofan individual optical fiber that is used to probe a single region in thetissue. In some cases, the numerical aperture of the individual opticalfiber is 90% or less, e.g., 80% or less, 75% or less, 70% or less, 65%or less, and is 10% or more, 20% or more, 30% or more, 40% or more, 50%or more, including 60% or more, of the objective numerical aperture. Insome cases, the numerical aperture of the individual optical fiber is inthe range of 10% to 90%, e.g., 20% to 80%, 30% to 75%, 40% to 70%,including 50% to 65%, of the objective numerical aperture. In somecases, the numerical aperture of the individual optical fiber is 0.01 ormore, e.g., 0.1 or more, 0.2 or more, 0.3 or more, including 0.4 ormore, and is 1.4 or less, e.g., 1.2 or less, 1.0 or less, 0.8 or less,0.6 or less, including 0.5 or less. In certain embodiments, thenumerical aperture of the individual optical fiber is in the range of0.01 to 1.4, e.g., 0.1 to 1.0, 0.2 to 0.8, including 0.3 to 0.6.

The number of optical fibers that form the optical fiber bundle, each ofwhich are used to direct light stimulus from the objective and toprovide illumination to an individual region of the target tissue, mayvary, and may be any suitable number. In some cases, the number ofoptical fibers in the optical fiber bundle is one or more, e.g., 2 ormore, 3 or more, 4 or more, 5 or more, 6 or more, 7 or more, including10 or more, and is 100 or less, e.g., 80 or less, 60 or less, 40 orless, 20 or less, 15 or less, 10 or less, 8 or less, 7 or less, 6 orless, including 5 or less. In certain embodiments, the number of opticalfibers is in the range of 1 to 100, e.g., 2 to 60, 3 to 40, 4 to 20,including 4 to 10.

The optical fiber end that is implanted into the target tissue may haveany suitable configuration suitable for illuminating a region of thetissue with a light stimulus delivered through the optical fiber and forcollecting fluorescence from the illuminated region.

In some cases, the optical fiber patchcord that directs the lightstimulus from the objective ends with an attachment device at each ofthe branched ends, where the attachment device is configured to connectto an optical fiber that is implanted in the target tissue. Any suitableattachment device may be used. In some cases, the attachment deviceincludes a ferrule, e.g., a metal, ceramic or plastic ferrule. Theferrule may have any suitable dimensions. In some cases, the ferrule hasa diameter in the range of 0.5 to 3 mm, e.g., 0.75 to 2.5 mm, or 1 to 2mm.

The image detector may be any suitable image detector. In someinstances, the image detector is a digital camera, such as acomplementary metal-oxide-semiconductor (CMOS) camera (e.g., ascientific CMOS (sCMOS) camera), or a charge-coupled device (CCD) camera(e.g., an electron-multiplying CCD (EMCCD) camera). In some cases, theimage detector includes an image sensor, which is configured to detectlight directed to the image detector by the optical fiber.

The present system may include any suitable electronic components tocontrol and/or coordinate the various optical components. The opticalcomponents of the present system may be controlled by a controller,e.g., to coordinate the illumination unit illuminating the sample withlight pulses of different wavelengths and/or the recording of the imagewith the image detector. The controllers may include a driver for thelight sources that control the intensity and/or frequency of the lightpulses. The controller (e.g., the driver for the light sources) may alsobe configured to control the wavelength of light emitted from anindividual light source. The controllers may be in communication withcomponents of the illumination unit (e.g. the light sources,collimators, shutters, filter wheels, moveable mirrors, lenses, etc.)and the image detector.

In some embodiments, the present system includes a computational unitconfigured to control and/or coordinate the light stimulus and imagecapture through one or more controllers, and to analyze images recordedby the image detector. A computational unit of the present system mayinclude any suitable components to analyze the recorded images. Thus,the system may include one or more of the following: a processor; anon-transient, computer-readable memory, such as a computer-readablemedium; an input unit, such as a keyboard, mouse, touchscreen, etc.; anoutput unit, such as a monitor, screen, speaker, etc.; a networkinterface, such as a wired or wireless network interface; and the like.

In some cases, the system may include a computer-readable mediumcontaining instructions that can be executed by a processor, which inturn causes the system to perform any suitable portion of a method ofthe present disclosure, using components of the system.

Methods

A general implementation of a method of the present disclosure mayinclude first illuminating a region or several regions of a targettissue (e.g., several distinct regions of the target tissue) with alight stimulus. The light stimulus includes light centered around asuitable wavelength and pulsed at a known interval to generate agenerally intermittent pattern of illumination for a particularwavelength. The light may be pulsed at a regular interval, defined by afrequency and a pulse length. The light pattern may also be defined by aduty cycle, where the duty cycle is the percentage of a time periodduring which a signal, i.e., the light, is on.

The light stimulus may include a first set of light pulses at a firstwavelength, and a second set of light pulses at one or more wavelengths.In some cases, the first wavelength is different from the one or morewavelengths in the second set of light pulses. The second set of lightpulses may include one or more subsets of light pulses, each subsethaving a wavelength. In some instances, the second set of light pulsesincludes two or more subsets of light pulses, each subset having adifferent wavelength. The second set of light pulses may include a firstsubset of light pulses at a second wavelength, and the second set oflight pulses may further include a second subset of light pulses at athird wavelength, and so on up until any suitable number of subsets oflight pulses. In some cases, the wavelength of the light pulses of thefirst set is a different wavelength from the one or more wavelengths oflight pulses of the second set. For example, the wavelength of the lightpulses of the first set is a different wavelength from the secondwavelength, and the wavelength of the light pulses of the first set is adifferent wavelength from the third wavelength.

The light pulses of the first set and the light pulses of the second setmay be timed so that they do not overlap with each other. Thus, in somecases, each light pulse of the first set is interleaved among lightpulses of the second set. In some cases, light pulses of the first setand light pulses of the second set alternate one after another (FIG. 1A,lower left inset, where 410 nm light pulses alternate with 470 nm lightpulses). In some cases, the light pulses of the first set are timed tobe at every other interval between light pulses of the second set (i.e.,at half the frequency of the light pulses of the second set). Any othersuitable relative timing of light pulses of the first set and second setmay be used, where the light pulses of the first set and the lightpulses of the second set do not overlap with each other. Light pulses ofdifferent subsets of the second set may be timed to be synchronous,simultaneous, and/or may be overlapping, or may not be overlapping.

The light stimulus is delivered to a region in a tissue of interest by alight conduit that includes one or more optical fibers, e.g., one ormore multimode optical fibers, where one end of the conduit collects thelight stimulus (e.g., light stimulus generated by an illumination unitand focused with an objective, as described above) and the other end isconfigured to illuminate the region in the tissue with the lightstimulus. For example, the other end of the conduit may be configured tobe implanted into the tissue at the region to illuminate the region withthe light stimulus.

Each region illuminated by the light stimulus may contain excitablecells, e.g., neurons that contain one or more cellular electricalactivity-dependent fluorescent moieties, e.g., neural activity-dependentfluorescent moieties, such as a genetically-encoded calcium indicator.Thus, the cells labeled with a cellular electrical activity-dependentfluorescent moiety may emit fluorescent when stimulated by a lightstimulus of an appropriate wavelength and intensity, where the intensityof the fluorescence depends on the electrical activity of the cell. Insome cases, an electrically active cell, e.g., a more depolarized cell,labeled with a cellular electrical activity-dependent fluorescent moietywill emit a stronger fluorescence when stimulated by a light stimulus atthe excitation wavelength of the activity-dependent fluorescent moietyand having sufficient intensity compared to a cell that is notelectrically active, e.g., a more hyperpolarized cell, labeled with theactivity-dependent fluorescent moiety and stimulated by the same lightstimulus. Depending on the wavelength of the light pulses, the regionmay emit fluorescence that is activity-dependent, oractivity-independent.

The wavelength of light pulses of the second set may be at an excitationwavelength of a cellular electrical activity-dependent fluorescentmoiety in the cells of the region illuminated by the light stimulus.Thus, a labeled cell in a region can emit a fluorescence that isrepresentative of the activity level of the cell when the region isilluminated by at least some of the light pulses of the second set.

The fluorescence emitted by the illuminated region can be collected bythe same optical fiber used to deliver the light stimulus, e.g., thesame optical fiber implanted at the illuminated region. Thus, a singleoptical fiber illuminates cells in a single region of the tissue ofinterest, and collects the fluorescence emitted by the labeled cells inthe region. When the region is illuminated by a light pulse having awavelength at the excitation wavelength of the activity-dependentfluorescent moiety, the collected fluorescence may be representative ofan average level of activity of the cells in the region.

The present method can include recording, at the end of the opticalfiber opposite the implanted end, the fluorescence collected at theimplanted end of the optical fiber. The recording may be done by animage detector (e.g., a digital camera) configured to capture an imageof the cross-section of the terminal end of the optical fiber. As theoptical fiber collects fluorescence representative of an average levelof activity of the cells in the region at the implanted end, thefluorescence emitted at the recording end is also representative of anaverage level of cellular activity of the region. In some instances, thefluorescence emitted at the recording end of the optical fiber does notpreserve the spatial information about the origin of fluorescence withrespect to individual cells within the region illuminated by the opticalfiber. Thus, the average level of fluorescence across the terminalcross-section of the optical fiber recorded by the image detector may beindicative of the aggregate activity of labeled cells in the illuminatedregion.

The image detector may be controlled to separately record at least oneimage for the duration of each light pulse. In other words, a set of oneor more images may be recorded for fluorescence emitted in response to alight pulse of the first set of light pulses, and a separate set of oneor more images may be recorded for fluorescence emitted in response to alight pulse (which may include one or more wavelengths of light pulsesfrom one or more subset of light pulses) of the second set of lightpulses. In some cases, a single image is recorded for each light pulse.In some cases, a single image is recorded for each light pulse of thesecond set of light pulses. Any other suitable timing of recording maybe used. Any number of images may be recorded to obtain an image stackthat shows a change in fluorescence emitted by the region of the targettissue over time.

The present method can include analyzing the recorded image, or aportion thereof, to obtain a measure of the cellular electrical activitylevel of the region of the target tissue. Any suitable method may beused to analyze the image. In some cases, the analyzing includesselecting a region of interest within which region the level offluorescence is to be measured. As the images can contain the terminalcross-section of the optical fibers, the analyzing may includedemarcating the terminal cross-section as the region of interest andmeasuring the fluorescence intensity within the terminal cross-section.The analyzing may include calculating the average intensity offluorescence over the region of interest. The analyzing may include anyother suitable data processing procedures, including, but limited to,background subtracting, normalizing, thresholding, curve fitting,subtracting bleaching artifacts, smoothing, etc., and combinationsthereof.

The target tissue may be any suitable target tissue that contains one ormore regions with electrically excitable cells. In some cases, thetarget tissue includes a plurality of regions with electricallyexcitable cells that are functionally interconnected, such thatelectrical activity in one region can modulate the electrical activityin another region. The electrically excitable cell may be any suitableelectrically excitable cell, including, but not limited to a neuron ormuscle cell. In some cases, the target tissue is neural tissue, e.g.,brain, spinal cord, etc. In some cases, the target tissue is the heart,gastrointestinal tract, lung, skeletal muscle, etc.

In some cases, the method further includes illuminating a region in atarget tissue with a first set of light pulses at the isosbestic pointof a cellular electrical activity-dependent fluorescent moiety used tolabel the excitable cells in the region. The fluorescence signal emittedin response to the first set of light pulses may then be independent ofthe level of electrical activity of the excitable cell. Thus, therecorded trace of the fluorescence signal obtained at the isosbesticpoint of the cellular electrical activity-dependent fluorescent moietymay serve as a control to correct for, e.g., subtract out, thenon-cellular electrical activity-related component in the measuredcellular electrical activity-dependent fluorescence level.

In certain embodiments, the present method further includes illuminatinga region in a target tissue, where the region includes neurons thatcontain either one or both of two cellular electrical activity-dependentfluorescent moieties and the two activity-dependent fluorescent moietieshave different (and distinguishable) excitation and emissionwavelengths. Thus, the second set of light pulses used to illuminate theregion may include two subsets of light pulses at different wavelengths,each of which is at the excitation wavelength of one or the otheractivity-dependent fluorescent moiety. Light pulses of the two subsetsmay be simultaneous, synchronous, or non-overlapping. The fluorescenceemitted from the illuminated region may include fluorescence at twowavelengths, each of which may be representative of cellular electricalactivity in the cell that is labeled with the activity-dependentfluorescent moiety that produced the respective fluorescence. Thus, insome cases, a first collection of cells may be labeled with a firstactivity-dependent fluorescent moiety, which emits fluorescence at afirst wavelength that is representative of cellular electrical activityin the first collection of cells, and a second collection of cells maybe labeled with a second activity-dependent fluorescent moiety, whichemits fluorescence at a second wavelength that is representative ofcellular electrical activity in the second collection of cells. Theactivity-dependent fluorescence at the two different wavelengths can becollected simultaneously with the optical fiber (e.g., multimode opticalfiber) that illuminated the region, and the combined fluorescence can bedirected to the image detector and recorded. In some cases, thefluorescence emitted from the region is split, e.g., using an imagesplitter, to from separate images for the fluorescence emitted by thecells expressing the first activity-dependent fluorescent moiety and forthe fluorescence emitted by the cells expressing the secondactivity-dependent fluorescent moiety. Thus, the method may includerecording a first image of the terminal cross-section of the opticalfiber for a region, where the a cross-sectional average of thefluorescence is representative of an aggregate neural activity of afirst collection of neurons labeled with the first neuralactivity-dependent fluorescent moiety, and a second image of theterminal cross-section of the optical fiber for a region, where the across-sectional average of the fluorescence is representative of anaggregate neural activity of a second collection of neurons labeled withthe second neural activity-dependent fluorescent moiety. As such, theaggregate neural activities of the first collection of neurons and thesecond collection of neurons measured by the present method arecontemporaneous aggregate neural activities. Where a region in a targettissue contains neurons that are labeled with multiple neuralactivity-dependent fluorescent moieties, all or at least some of thefluorescent moieties may share the same isosbestic point.

In some cases, the method includes illuminating a plurality of regionsof a target tissue using a plurality of optical fibers, where eachregion contains a plurality of excitable cells, e.g., neurons, labeledwith a cellular electrical activity-dependent fluorescent moiety, andwhere one optical fiber illuminates and collects fluorescence from oneregion. The recording may include simultaneously recording onto a frameof the image detector the terminal cross-sections of each of the opticalfibers, where each optical fiber terminal cross-section conveysfluorescence that is representative of a corresponding region in thetissue at which the optical fiber is implanted. For example, therecording may include simultaneously detecting using the image sensor ofthe image detector light from the terminal cross-sections of each of theoptical fibers. As described herein, the light detected by the imagesensor may include fluorescence generated in response to the lightpulses used to excite the neural activity-dependent fluorescent moietiesin the region of interest.

The number of optical fibers used in the present method may vary, andmay be any suitable number. In some cases, the number of optical fibersused to excite and image different regions of the target tissue is oneor more, e.g., 2 or more, 3 or more, 4 or more, 5 or more, 6 or more, 7or more, including 10 or more, and is 100 or less, e.g., 80 or less, 60or less, 40 or less, 20 or less, 15 or less, 10 or less, 8 or less, 7 orless, 6 or less, including 5 or less. In certain embodiments, the numberof optical fibers is in the range of 1 to 100, e.g., 2 to 60, 3 to 40, 4to 20, including 4 to 10.

Any suitable optical fibers may be used in the present method. Theoptical fiber may be a multimode optical fiber. The optical fiber mayinclude a core defining a core diameter, where light passes through thecore. The core may be further surrounded by a cladding. The corediameter of an individual optical fiber that is used to probe a singleregion in the tissue may vary, and may be 10 μm or more, e.g., 50 μm ormore, 100 μm or more, 200 μm or more, including 300 μm or more, and maybe 1,000 μm or less, e.g., 900 μm or less, 800 μm or less, 700 μm orless, including 600 μm or less. In some embodiments, the core diameterof the individual optical fiber may be in the range of 10 to 1,000 μm,e.g., 50 to 1,000 μm, 100 to 1,000 μm, 200 to 800 μm, including 300 to600 μm.

The numerical aperture of an individual optical fiber that is used toprobe a single region in the tissue may vary, and can be less than thenumerical aperture of the objective. In some cases, the numericalaperture of the individual optical fiber is 90% or less, e.g., 80% orless, 75% or less, 70% or less, 65% or less, and is 10% or more, 20% ormore, 30% or more, 40% or more, 50% or more, including 60% or more, ofthe objective numerical aperture. In some cases, the numerical apertureof the individual optical fiber is in the range of 10% to 90%, e.g., 20%to 80%, 30% to 75%, 40% to 70%, including 50% to 65%, of the objectivenumerical aperture. In some cases, the numerical aperture of theindividual optical fiber is 0.01 or more, e.g., 0.1 or more, 0.2 ormore, 0.3 or more, including 0.4 or more, and is 1.4 or less, e.g., 1.2or less, 1.0 or less, 0.8 or less, 0.6 or less, including 0.5 or less.In certain embodiments, the numerical aperture of the individual opticalfiber is in the range of 0.01 to 1.4, e.g., 0.1 to 1.0, 0.2 to 0.8,including 0.3 to 0.6.

The present method may use any suitable image detector. In someinstances, the image detector is a digital camera, such as a CMOS camera(e.g., a sCMOS camera), or a charge-coupled device (CCD) camera (e.g.,an electron-multiplying CCD (EMCCD) camera).

The collection of neurons whose activity is to be measured by thepresent method may be any suitable collection of neurons. In some cases,a collection of neurons is defined by a known functional classification.Any convenient functional classification may be used to define thecollection of neuron. In some cases, the collection of neurons includesexcitatory neurons, inhibitory neurons, sensory neurons, motor neurons,interneurons, etc. In some cases, the collection of neurons includesdopaminergic, cholinergic, GABAergic, glutamatergic, or peptidergicneurons. In some cases, the collection of neurons includes Purkinjecells, pyramidal cells, golgi cells, Lugaro cells, basket cells,candelabrum cells, granule cells, stellate cells, unipolar brush cells,medium spiny neurons, Renshaw cells, spindle cells, etc. The differentfunctional cells may be labeled specifically with a cellular electricalactivity-dependent fluorescent moiety using any suitable method. In somecases, a cell-specific promoter, or a combination of differentcell-specific promoters, may be used to control expression of agenetically-encoded cellular electrical activity-dependent fluorescentmoiety, e.g., a genetically-encoded calcium indicator, specifically in afunctionally-defined collection of neurons.

The target tissue can be a human target tissue (e.g., an in vivo, invitro, or ex vivo target tissue). The target tissue can be a non-humananimal target tissue (e.g., an in vivo, in vitro, or ex vivo targettissue). Non-human animals include non-human primates, murines (e.g.,rats, mice), lagomorphs (e.g., rabbits), ungulates, felines, canines,and the like. The target tissue can be in a live human or non-humananimal. The target tissue can be in a freely-moving human or non-humananimal.

The present method may include illuminating any suitable region of thetarget tissue, e.g., the brain. In some cases, the method includesilluminating a functionally and/or anatomically defined region of abrain, e.g., a amphibian brain, a reptile brain, a bird brain, amarsupial brain, mammalian brain, etc. In some cases, the methodincludes illuminating at least of portion of the ventral tegmental area(VTA), prefontal cortex (PFC), nucleus accumbens (NAc), amygdala (BLA),substantia nigra, ventral pallidum, globus pallidus, dorsal striatum,ventral striatum, subthalamic nucleus, hippocampus, dentate gyrus,cingulate gyrus, entorhinal cortex, olfactory cortex, sensory cortex,thalamus, primary motor cortex, and cerebellum, etc., of a mammalianbrain. Any other suitable functionally and/or anatomically definedregion of a mammalian brain may be illuminated in the present method.

In some cases, the method includes illuminating a region of the brainwhere the cell body of labeled neurons is present. In some cases, themethod includes illuminating a region of the brain where the neuronalprojections, e.g., axonal projections, dendritic projections, etc., oflabeled neurons are present.

In some cases, where two or more regions are illuminated and whosecellular electrical activities are recorded, the method includesilluminating regions that are functionally distinct. Two regions may befunctionally distinct by being two distinct anatomical regions. Tworegions may be functionally distinct by containing different functionaltypes of population of neurons. Two regions may be functionally distinctby having distinct types of inputs or outputs to other regions of thebrain, and/or different functional types of neurons. Two regions may befunctionally distinct by any other suitable criteria.

In some cases, two or more regions that are illuminated and whosecellular electrical activity is recorded by the present method may befunctionally connected regions of the target tissue, e.g., the brain. Afunctionally connected regions of the brain may have neurons from oneregion that are connected on average to neurons of a second region by aminimum number of synaptic connections of one or more, e.g., two ormore, 3 or more, 4 or more, including 5 or more, and by a minimum numberof synaptic connections of 10 or less, 9 or less, 8 or less, 7 or less,6 or less 5 or less, 4 or less, including 3 or less.

In some embodiments, the target tissue whose region(s) are illuminatedand whose cellular electrical activity is recorded by the present methodis an in vivo tissue, or an ex vivo tissue (e.g., a tissue slice). Insome cases, the target tissue is in a freely moving animal, or is in ahead-fixed animal. In some cases, the target tissue is in an animal thathas been exposed to an environmental manipulation. In some cases, thetarget tissue is in an animal that has been conditioned to respond,behaviorally and/or neurologically, more reliably to a stimulus comparedto an animal that has not been conditioned. In some cases, the animal isa water-deprived animal; a water-deprived animal rewarded with water; afood-deprived animal; a food-deprived animal rewarded with food; asolitary animal; an animal in the presence of another animal of the samespecies; an animal presented with an aversive stimulus, e.g., anelectric shock, aversive sounds, such as a loud noise, extremetemperatures, repulsive odors, etc.; an animal presented with a novelobject; an animal navigating a maze; an animal performing amemory/recollection task; etc.

The present method may employ any suitable frequency of light pulses. Insome cases, the frequency of the light pulses is 0.1 Hz or more, e.g., 1Hz or more, 5 Hz or more, 10 Hz or more, 15 Hz or more, 20 Hz or more,including 25 Hz or more, and is 1,000 Hz or less, e.g., 500 Hz or less,200 Hz or less, 100 Hz or less, 80 Hz or less, including 60 Hz or less.In certain embodiments, the frequency of the light pulses is in therange of 0.1 to 1,000 Hz, e.g., 1 to 500 Hz, 1 to 200 Hz, 5 to 80 Hz, 10to 60 Hz, including 15 to 60 Hz.

The present method may employ any suitable duration of a pulse of lightto illuminate a region in a target tissue. In some cases, the durationof a light pulse is 1.0 ms or more, e.g., 2.0 ms or more, 5.0 ms ormore, 10.0 ms or more, 15 ms or more, 20 ms or more, including 25 ms ormore, and is 1,000 ms or less, e.g., 500 ms or more, 300 ms or less, 200ms or less, 100 ms or less, 50 ms or less, including 40 ms or less. Insome embodiments, the duration of a light pulse is in the range of 1.0to 1,000 ms, e.g., 2.0 to 500 ms, 5.0 to 200 ms, 10.0 to 100 ms,including 15 to 50 ms.

The present method may employ any suitable duty cycle for the pulse oflight used to illuminate a region in a target tissue. In some cases, theduty cycle of the light pulse is 5% or more, such as 10% or more, or 15%or more or 20% or more, or 25% or more, or 30% or more, or 35% or more,or 40% or more, or 45% or more, or 50% or more, or 55% or more, or 60%or more, or 65% or more, or 70% or more, or 75% or more, including 100%or less, such as 95% or less, or 90% or less, or 85% or less, or 80% orless, or 75% or less, or 70% or less, or 65% or less, or 60% or less, or55% or less, or 50% or less. In some embodiments, the duty cycle of thelight pulse is in the range of 5% to 75%, such as 10% to 70%, or 10% to65%, or 10% to 60%, or 10% to 55%, or 10% to 50%, or 15% to 45%, or 15%to 40%, or 15% to 35%, or 20% to 30%. In certain instances, the dutycycle of the light pulse is 25%.

The power of the light pulses used to illuminate a region of a targettissue may be any suitable power. The power of the light pulse may bethe power measured at the end of the patchcord, i.e., at the end of theoptical fiber at the surface of the target tissue. In some cases, alight pulse for exciting a cellular electrical activity-dependentfluorescent moiety has a power of 0.5 μW or more, e.g., 1.0 μW or more,2.0 μW or more, 3.0 μW or more, 5 μW or more, 10 μW or more, 15 μW ormore, including 20 μW or more, and has a power of 500 μW or less, e.g.,250 μW or less, 200 μW or less, 150 μW or less, 100 μW or less, 50 μW orless, including 30 μW or less. In some cases, a light pulse for excitinga cellular electrical activity-dependent fluorescent moiety has a powerin the range of 0.5 to 500 μW, e.g., 1.0 to 250 μW, 1.0 to 200 μW, 2.0to 100 μW, 3.0 to 50 μW, including 3.0 to 30 μW. In some cases, a lightpulse for exciting a cellular electrical activity-dependent fluorescentmoiety has a power of 0.5 mW or more, e.g., 1.0 mW or more, 2.0 mW ormore, including 5.0 mW or more, and has a power of 10 mW or less, e.g.,8.0 mW or less, 6.0 mW or less, 4.0 mW or less, including 3.0 mW orless. In some cases, a light pulse for exciting a cellular electricalactivity-dependent fluorescent moiety has a power in the range of 0.5 to10 mW, e.g., 1.0 to 8.0 mW, including 1.0 to 6.0 mW.

In some embodiments, a region illuminated by the light stimulus maycontain excitable cells, e.g., neurons, that contain one or morelight-activated polypeptides, e.g., light-activated ion channels or ionpumps, which, when activated by a light pulse at the activationwavelength, can modulate the electrical activity of the cells. Thelight-activated polypeptide may be any suitable light-activatedpolypeptide for modulating the activity of an excitable cell in alight-dependent manner, as described further below. The light-activatedpolypeptide may be a genetically encoded light-activated polypeptideexpressed in the cell.

The region that is illuminated by an optical fiber, according toembodiments of the present method, may contain cells that contain both acellular electrical activity-dependent fluorescent moiety and alight-activated polypeptide, or may contain cells that have either oneof the two. Thus, the region may contain a first collection of cellsthat are labeled with the cellular electrical activity-dependentfluorescent moiety, and a second collection of cells that contain thelight-activated polypeptide. The first collection of cells and thesecond collection of cells may be substantially the same collection ofcells (i.e., the cells in the region contain both the cellularelectrical activity-dependent fluorescent moiety and the light-activatedpolypeptide, if any). Alternatively, the first collection of cells andthe second collection of cells may be distinct but overlappingcollections of cells (i.e., some cells in the region contain both thecellular electrical activity-dependent fluorescent moiety and thelight-activated polypeptide, while other cells in the region containeither the cellular electrical activity-dependent fluorescent moiety orthe light-activated polypeptide, if any). In some cases, the firstcollection of cells and the second collection of cells may besubstantially non-overlapping collections of cells (i.e., the cells inthe region contain either the cellular electrical activity-dependentfluorescent moiety or the light-activated polypeptide, if any). Thecells expressing the light-activated polypeptide may be afunctionally-defined population of cells, as described elsewhere.

Where the region contains a collection of cells containing alight-activated polypeptide, the wavelength of the first set of lightpulses may be at the activation wavelength of the light-activatedpolypeptide. The power of the light pulses at the activation wavelengthof the light-activated polypeptide may be any suitable power foractivating the light-activated polypeptide and modulating cellularelectrical activity in the region. In some cases, the power of the lightpulses at the activation wavelength of the light-activated polypeptideis 0.01 mW or more, e.g., 0.05 mW or more, 0.1 mW or more, 0.5 mW ormore, 1.0 mW or more, 5.0 mW or more, including 10.0 mW or more, and is50 mW or less, e.g., 40 mW or less, 30 mW or less, 20 mW or less, 10 mWor less, 5.0 mW or less, 4.0 mW or less, 3.0 mW or less, 2.0 mW or less,including 1 mW or less. In some cases, the power of the light pulses atthe activation wavelength of the light-activated polypeptide is in therange of 0.01 to 50 mW, e.g., 0.05 to 5.0 mW, 0.1 mW to 4.0 mW,including 0.1 mW to 3 mW.

In some cases, the power of the light pulses at the activationwavelength of the light-activated polypeptide is sufficient to generateelectrical activity in the cell that approximates electrical activitythat is generated by a natural stimulus, i.e., a stimulus that isprovided to the animal in which the target tissue resides as a whole,rather than specifically only to those cells that contain thelight-activated polypeptide in the form of a light pulse. A naturalstimulus may be a sensory stimulus provided to a sensory organ of theanimal, such as, but not limited to, light to the visual system, tactilestimulus to the somatosensory system, sound to the auditory system,tastant to the gustatory system, odor to the olfactory system, etc. Insome cases the natural stimulus is a reward stimulus, e.g., a waterreward and/or food reward. In some cases, the natural stimulus is anaversive stimulus, e.g., an electric shock, aversive sounds, such as aloud noise, extreme temperatures, repulsive odors, etc. In some cases,the natural stimulus is a novel object. In some cases, the naturalstimulus is a social cue. In some cases, the natural stimulus is a task,such as navigating a maze or performing a memory/recollection task, etc.

The activation of the light-activated polypeptide using the appropriatewavelength and power of light pulse may induce electrical activity inthe cell that has a similar maximum magnitude of response as theelectrical activity induced by a natural stimulus, as measured by thelevel of fluorescence from a neural activity-dependent fluorescentmoiety expressed in the same cell. The cellular electrical activityinduced by activation of the light-activated polypeptide may have amaximum magnitude that is 50% or more, e.g., 60% or more, 70% or more,80% or more, 90% or more, 95% or more, including 100% or more, and is200% or less, e.g., 150% or less, 120% or less, 110% or less, including100% or less than the maximum magnitude of the cellular electricalactivity induced by a natural stimulus. In some cases, the cellularelectrical activity induced by activation of the light-activatedpolypeptide may have a maximum magnitude in the range of 50 to 200%,e.g., 60 to 150%, 70 to 120%, including 80 to 110% of the maximummagnitude of the cellular electrical activity induced by a naturalstimulus. In some cases, the cellular electrical activity induced byactivation of the light-activated polypeptide may have a duration ofresponse above background that is 50% or more, e.g., 60% or more, 70% ormore, 80% or more, 90% or more, 95% or more, including 100% or more, andis 200% or less, e.g., 150% or less, 120% or less, 110% or less,including 100% or less than the duration of response above background ofthe cellular electrical activity induced by a natural stimulus. In somecases, the cellular electrical activity induced by activation of thelight-activated polypeptide may have a duration of response abovebackground in the range of 50 to 200%, e.g., 60 to 150%, 70 to 120%,including 80 to 110% of the duration of response above background of thecellular electrical activity induced by a natural stimulus. In somecases, the cellular electrical activity induced by activation of thelight-activated polypeptide may have a response latency that is 50% ormore, e.g., 60% or more, 70% or more, 80% or more, 90% or more, 95% ormore, including 100% or more, and is 200% or less, e.g., 150% or less,120% or less, 110% or less, including 100% or less than the responselatency of the cellular electrical activity induced by a naturalstimulus. In some cases, the cellular electrical activity induced byactivation of the light-activated polypeptide may have a responselatency in the range of 50 to 200%, e.g., 60 to 150%, 70 to 120%,including 80 to 110% of the response latency of the cellular electricalactivity induced by a natural stimulus.

In some cases, where the region contains a first collection of cellscontaining a light-activated polypeptide and a second collection ofcells labeled with an electrical activity-dependent fluorescent moiety,the light pulse having a wavelength at the excitation wavelength of theelectrical activity-dependent fluorescent moiety has a power that issufficiently low that the light pulse does not cause activation of thelight-activated polypeptide to significantly modulate electricalactivity of the cell, as measured by the fluorescence from theelectrical activity-dependent fluorescent moiety. In some cases, thelight pulse having a wavelength at the excitation wavelength of theelectrical activity-dependent fluorescent moiety has a power of 50 μW orless, e.g., 30 μW or less, 15 μW or less, 10 μW or less, including 8.0μW or less, and has a power of 0.5 μW or more, e.g., 1.0 μW or more, 2.0μW or more, including 3.0 μW or more. In some cases, the light pulsehaving a wavelength at the excitation wavelength of the electricalactivity-dependent fluorescent moiety has a power in the range of 0.5 to50 μW, e.g., 1.0 to 30 μW, 1.0 to 15 μW, 1.0 to 10 μW, including 1.0 to8 μW.

The region may contain any suitable number of distinct collections ofcells, where each collection of cells is labeled with a differentelectrical activity-dependent fluorescent moiety. In some cases, theregion contains 1 or more, e.g., 2 or more, 3 or more, including 4 ormore, distinct collections of cells, and contains 10 or fewer, e.g., 9or fewer, 8 or fewer, 7 or less, 6 or fewer, including 5 or fewerdistinct collections of cells. In some cases, the region contains in therange of 1 to 10, e.g., 1 to 8, 2 to 6, 2 to 5, including 2 to 4collections of cells. In some cases, the method includes illuminatingthe region with a light stimulus containing light pulses at anexcitation wavelength for some or all of the different electricalactivity-dependent fluorescent moieties in the region. For example, amultimode optical fiber as described herein may be used to illuminatethe region with a light stimulus containing two or more light pulses atdifferent excitation wavelengths for different electricalactivity-dependent fluorescent moieties in the region.

The present method can be a rapid method of measuring cellularelectrical activity, e.g., neural activity, in one or more regions of atarget tissue, e.g., a brain. In some cases, the present method providesreal-time measurement of cellular electrical activity, in one or moreregions of a target tissue. In some cases, the method can be performedin 20 ms or less, e.g., 10 ms or less, 8 ms or less, 6 ms or less, 5 msor less, 4 ms or less, including 3 ms or less, and can be performed in 1ms or more, 2 ms or more, 3 ms or more, including 4 ms or more. In somecases, the method can be performed in a range of 1 to 20 ms, e.g., 1 to10 ms, 2 to 8 ms, including 2 to 6 ms. In some cases, the aggregateneural activity of 2 or more, e.g., 3 or more, 5 or more, 7 or more,including 10 or more, and 50 or less, e.g., 30 or less, 20 or less,including 15 or less regions of a target tissue can be analyzedsynchronously using the present method in 20 ms or less, e.g., 10 ms orless, 8 ms or less, 6 ms or less, 5 ms or less, 4 ms or less, including3 ms or less, and can be performed in 1 ms or more, 2 ms or more, 3 msor more, including 4 ms or more. In some cases, the aggregate neuralactivity of 2 or more, e.g., 3 or more, 5 or more, 7 or more, including10 or more, and 50 or less, e.g., 30 or less, 20 or less, including 15or less regions of a target tissue can be analyzed synchronously usingthe present method in 1 to 20 ms, e.g., 1 to 10 ms, 2 to 8 ms, including2 to 6 ms.

In some embodiments, the method is a method for closed-loop control ofcellular electrical activity in a target tissue. In some cases, where afirst region of the target tissue contains a collection of cellscontaining a light-activated polypeptide, the method further includesilluminating the first region with the cells containing alight-activated polypeptide with a light pulse at the activationwavelength of the light-activated polypeptide, where the timing and/orpower of the illuminating the first region with the cells containing alight-activated polypeptide is based on an recorded image of a terminalcross-section of an optical fiber from a second region and the analysisof the aggregate neural activity in the second region. Thus, in somecases, the analysis of the aggregate neural activity in the secondregion may indicate that first region should be illuminated by a lightpulse to activate a depolarizing light-activated polypeptide at acertain intensity and for a specific duration, e.g., to compensate for alack of activity in the second region. In some cases, the analysis ofthe aggregate neural activity in the second region may indicate thatfirst region should be illuminated by a light pulse to activate ahyperpolarizing light-activated polypeptide at a certain intensity andfor a specific duration, e.g., to reduce hyperactivity in the secondregion.

Cellular Electrical Activity-Dependent Fluorescent Moieties

The cellular electrical activity-dependent fluorescent moieties, e.g.,the neural activity-dependent fluorescent moieties, may include anysuitable fluorescent moiety whose fluorescence properties are responsiveto the electrical activity of the cell in which it resides. Fluorescentmoieties whose fluorescence properties are sensitive to cellularelectrical activity include ratiometric/non-ratiometric dyes andfluorescent proteins. Fluorescent moieties whose fluorescence propertiesare sensitive to cellular electrical activity may be a fluorescenceresonance energy transfer (FRET)-based reporter. Fluorescent moietieswhose fluorescence properties are sensitive to cellular electricalactivity may be sensitive to changes in intracellular concentration ofions such as calcium, sodium and protons or to changes in membranepotential. In such cases, fluorescent dyes of interest include, but arenot limited to, calcium indicator dyes (Indo-1, Fura-2, and Fluo-3,Calcium Green®, Fluo-4, etc.); sodium indicator dyes (sodium-bindingbenzofuran isophthalate (SBFI), Sodium Green™, CoroNa™ Green, CoroNa™Red, etc.); and proton indicator dyes(2′,7′-bis-(carboxyethyl)-5-(and-6)-carboxyfluorescein (BCECF), etc.).

Cellular electrical activity-dependent fluorescent proteins of interestinclude, but are not limited to, genetically encoded calcium indicators(Cameleon, Pericam, TN-XXL, Twitch, GECO, GCaMP1, GCaMP2, GCaMP3, GCaMP6and derivatives thereof, as well as those cited in U.S. Pat. No.8,629,256, and Tian et al. 2012 Prog Brain Res, 196:79, which areincorporated herein by reference); and genetically encoded voltageindicators (QuasAr1, QuasAr2, VSFP, and derivatives thereof, as well asthose cited in US App. Pub. No. 2013/0224756, Hochbaum et al., NatMethods 2014 11:825, Baker et al. Brain Cell Biol 2008 36:53; and Mutohet al., Exp Physiol 2011 96:13, each of which are incorporated herein byreference). Other suitable GCaMP-based genetically encoded calciumindicators include GCaMP2.1, GCaMP2.2a, GCaMP2.2b, GCaMP2.3, GCaMP2.4,GCaMP3, GCaMP5g, GCaMP6m, GCaMP6s, GCaMP6f, etc. Suitable GECO-basedgenetically encoded calcium indicators include G-GECO1, G-GECO1.1 andG-GECO1.2, the red fluorescing indicator R-GECO1, the blue fluorescingindicator B-GECO1, the emission ratiometic indicator GEM-GECO1, and theexcitation ratiometric GEX-GECO1, etc.

A suitable genetically encoded calcium indicator polypeptide cancomprise an amino acid sequence having at least 75%, at least 80%, atleast 85%, at least 90%, at least 95%, at least 98%, at least 99%, or100%, amino acid sequence identity with an amino acid sequence set forthin FIG. 13A-13S. A suitable genetically encoded calcium indicatorpolypeptide can comprise an amino acid sequence having at least 75%, atleast 80%, at least 85%, at least 90%, at least 95%, at least 98%, atleast 99%, or 100%, amino acid sequence identity with an amino acidsequence set forth in FIGS. 14A-14C.

In some cases, the fluorescent moiety may be sensitive to biochemicalchanges in the excitable cell, such as changes in enzymatic activity(e.g., activation of kinases); changes in binding interactions (e.g.,binding of transcription factors to DNA); changes in subcellularlocalization of proteins; etc. Exemplary fluorescent moieties arefurther described in, e.g, Mehta et al., Annu Rev Biochem. 2011; 80:375, which is incorporated herein by reference.

Light-Activated Polypeptides

Where region of the target tissue includes cells that contain alight-activated polypeptide, the light-activated polypeptide may be anysuitable light-activated polypeptide for modulating the electricalactivity of the cell with a light stimulus. In some instances, thelight-activated polypeptide is a light-activated ion channelpolypeptide. The light-activated ion channel polypeptides are adapted toallow one or more ions to pass through the plasma membrane of a targetcell when the polypeptide is illuminated with light of an activatingwavelength. Light-activated proteins may be characterized as ion pumpproteins, which facilitate the passage of a small number of ions throughthe plasma membrane per photon of light, or as ion channel proteins,which allow a stream of ions to freely flow through the plasma membranewhen the channel is open. In some embodiments, the light-activatedpolypeptide depolarizes the cell when activated by light of anactivating wavelength. In some embodiments, the light-activatedpolypeptide hyperpolarizes the cell when activated by light of anactivating wavelength. Suitable hyperpolarizing and depolarizingpolypeptides are known in the art and include, e.g., a channelrhodopsin(e.g., ChR2), variants of ChR2 (e.g., C128S, D156A, C128S+D156A, E123A,E123T), iC1C2, C1C2, GtACR2, NpHR, eNpHR3.0, C1V1, VChR1, VChR2, SwiChR,Arch, ArchT, KR2, ReaChR, ChiEF, Chronos, ChRGR, CsChrimson, and thelike. In some cases, the light-activated polypeptide includes bReaCh-ES,as described herein and described further in, e.g., Rajasethupathy etal., Nature. 2015 Oct. 29; 526(7575):653, which is incorporated byreference. Hyperpolarizing and depolarizing opsins have been describedin various publications; see, e.g., Berndt and Deisseroth (2015) Science349:590; Berndt et al. (2014) Science 344:420; and Guru et al. (Jul. 25,2015) Intl. J. Neuropsychopharmacol. 18:pyv079 (PMID 26209858).

As non-limiting examples, a suitable light-activated polypeptide cancomprise an amino acid sequence having at least 75%, at least 80%, atleast 85%, at least 90%, at least 95%, at least 98%, at least 99%, or100%, amino acid sequence identity with an amino acid sequence set forthin any one of FIG. 15A-15U. A bReaChES light-activated polypeptide cancomprise an amino acid sequence having at least 75%, at least 80%, atleast 85%, at least 90%, at least 95%, at least 98%, at least 99%, or100%, amino acid sequence identity with an amino acid sequence set forthin any one of FIG. 12B-12F.

Cells in a region of the target tissue may be labeled with a cellularactivity-dependent fluorescent moiety and/or the light-activatedpolypeptide may be introduced into the cells using any suitable method.In some cases, the cells in the region are genetically modified toexpress a genetically-encoded fluorescent moiety, e.g., agenetically-encoded calcium or voltage indicator, and/or alight-activated polypeptide. In some cases, the cells may be geneticallymodified using a viral vector, e.g., an adeno-associated viral vector,containing a nucleic acid having a nucleotide sequence that encodes thecellular activity-dependent fluorescent moiety and/or a light-activatedpolypeptide. The viral vector may include any suitable control elements(e.g., promoters, enhancers, recombination sites, etc.) to controlexpression of the cellular activity-dependent fluorescent moiety and/ora light-activated polypeptide according to cell type, timing, presenceof an inducer, etc.

Neuron-specific promoters and other control elements (e.g., enhancers)are known in the art. Suitable neuron-specific control sequencesinclude, but are not limited to, a neuron-specific enolase (NSE)promoter (see, e.g., EMBL HSENO2, X51956; see also, e.g., U.S. Pat. Nos.6,649,811, 5,387,742); an aromatic amino acid decarboxylase (AADC)promoter; a neurofilament promoter (see, e.g., GenBank HUMNFL, L04147);a synapsin promoter (see, e.g., GenBank HUMSYNIB, M55301); a thy-1promoter (see, e.g., Chen et al. (1987) Cell 51:7-19; and Llewellyn etal. (2010) Nat. Med. 16:1161); a serotonin receptor promoter (see, e.g.,GenBank S62283); a tyrosine hydroxylase promoter (TH) (see, e.g., Nucl.Acids. Res. 15:2363-2384 (1987) and Neuron 6:583-594 (1991)); a GnRHpromoter (see, e.g., Radovick et al., Proc. Natl. Acad. Sci. USA88:3402-3406 (1991)); an L7 promoter (see, e.g., Oberdick et al.,Science 248:223-226 (1990)); a DNMT promoter (see, e.g., Bartge et al.,Proc. Natl. Acad. Sci. USA 85:3648-3652 (1988)); an enkephalin promoter(see, e.g., Comb et al., EMBO J. 17:3793-3805 (1988)); a myelin basicprotein (MBP) promoter; a CMV enhancer/platelet-derived growth factor-βpromoter (see, e.g., Liu et al. (2004) Gene Therapy 11:52-60); a motorneuron-specific gene Hb9 promoter (see, e.g., U.S. Pat. No. 7,632,679;and Lee et al. (2004) Development 131:3295-3306); and an alpha subunitof Ca(²⁺)-calmodulin-dependent protein kinase II (CaMKIIα) promoter(see, e.g., Mayford et al. (1996) Proc. Natl. Acad. Sci. USA 93:13250).Other suitable promoters include elongation factor (EF) 1α and dopaminetransporter (DAT) promoters.

In some cases, cell type-specific expression of the cellularactivity-dependent fluorescent moiety and/or a light-activatedpolypeptide may be achieved by using recombination systems, e.g.,Cre-Lox recombination, Flp-FRT recombination, etc. Cell type-specificexpression of genes using recombination has been described in, e.g.,Fenno et al., Nat Methods. 2014 July; 11(7):763; and Gompf et al., FrontBehav Neurosci. 2015 Jul. 2; 9:152, each of which are incorporated byreference herein.

EXAMPLES

The following examples are put forth so as to provide those of ordinaryskill in the art with a complete disclosure and description of how tomake and use the disclosed subject matter, and are not intended to limitthe scope of what the inventors regard as their invention nor are theyintended to represent that the experiments below are all or the onlyexperiments performed. Efforts have been made to ensure accuracy withrespect to numbers used (e.g. amounts, temperature, etc.) but someexperimental errors and deviations should be accounted for. Unlessindicated otherwise, parts are parts by weight, molecular weight isweight average molecular weight, temperature is in degrees Celsius, andpressure is at or near atmospheric. Ø denotes the core diameter.Standard abbreviations may be used, e.g., bp, base pair(s); kb,kilobase(s); pl, picoliter(s); s or sec, second(s); min, minute(s); h orhr, hour(s); aa, amino acid(s); kb, kilobase(s); bp, base pair(s); nt,nucleotide(s); i.m., intramuscular(ly); i.p., intraperitoneal(ly); s.c.,subcutaneous(ly); and the like.

Example 1: Materials and Methods

The following materials and methods were used in the Examples.

Core Frame-Projected Independent-Fiber Photometry (FIP) Platform Setupand Modifications

The main FIP platform included a widefield microscope imaging a bundleof one or more (up to 7 in this example) fiber faces, with a series ofdichroic mirrors integrated in the microscope to be able tosimultaneously couple in various wavelength excitation light sources.Custom MATLAB® (Mathworks) software was used to control the timing ofthe various excitation light sources, to synchronously acquire cameraframes, and to digitally sum and compute the total fluorescence fromeach of the fibers in each camera frame in real-time. The excitationlight sources, dichroics, and acquisition timing protocols werereconfigurable to support combinations of dual-color recording,simultaneous recording and stimulation, and concurrent acquisition ofisosbestic control signals.

A custom patchcord of 7 bundled 400 μm Ø 0.48 numerical aperture (NA)fibers (Doric Lenses) was used for FIP experiments. One end of thepatchcord terminated in a SubMiniature version A (SMA) connector mounted(Thorlabs, SM1SMA) at the working distance of the objective, while theother end terminated in 7 individual 1.25 mm Ø stainless steel ferrules.These ferrules were coupled via ceramic sleeves (Thorlabs, ADAL1) to1.25 mm Ø ferrules implanted into a mouse.

The fiber faces were imaged through a 20×/0.75 NA objective (Nikon, CFIPlan Apo Lambda 20×) through a series of reconfigurable dichroicmirrors. Fluorescence emission from the fibers passed through a 535 nmbandpass fluorescence emission filter (selected for GCaMP recording;Semrock FF01-535/22-25). The fluorescence image was focused onto thesensor of a scientific complementary metal-oxide semiconductor (sCMOS)camera (Hamamatsu ORCA®-Flash4.0) through a tube lens (ThorlabsAC254-035-A-ML). The reconfigurable dichroic mirrors were mounted inremovable dichroic cube holders (Thorlabs, DFM1), and enabled two totallight sources to be coupled in. In the standard configuration, a 470 nmlight emitting diode (LED) (Thorlabs, M470F1), was fiber coupled intothe dichroic cube holder by using a 1000 μm Ø, 0.48 NA fiber (Thorlabs,M71L01) and a 405 nm, f=4.02 mm, 0.6 NA collimator (Thorlabs,F671SMA-405 and AD11F) with a 495 nm longpass dichroic mirror (Semrock,FF495-Di02-25×36). This produced an excitation spot of ˜2.5 mm Ø (10mm÷4.02 mm×1000 μm) at the working distance of the 20× objective (focallength of ˜10 mm). This spot was sufficiently large to fill all of thefibers of the 7-fiber branching patchcord. Typically the light powersemitted from the different fibers were within 25-50% of each other. Allof the LEDs used were controlled by a driver enabling digital modulationup to 1 kHz (Thorlabs, LEDD1B). See Example 2 for additional systemdesign, alignment, and calibration considerations.

Time-division multiplexing. To enable the concurrent recording ofmultiple channels per fiber (or for simultaneous optogeneticstimulation), a time-division multiplexing strategy was used totime-sequentially sample each channel individually. Schematics of thetime-division multiplexing strategy used for each experiment are shownin FIG. 1A, FIG. 8B, and FIG. 2F. Briefly, for GCaMP6 imaging,consecutive camera frames were captured using alternating 470 nm and 410nm excitation sources; i.e., every other camera frame was captured usingeither 470 nm or 410 nm light. For example if the camera is capturingimages at 40 Hz, the individual 470 nm and 410 nm signals are sampled at20 Hz. For simultaneous GCaMP6 and R-CaMP2 imaging, camera frames werecaptured using alternating excitation sources of either 470 nm+560 nm or410 nm alone. For simultaneous GCaMP6 imaging and optogeneticstimulation, camera frames were captured only with 470 nm excitationlight, and additional 470 nm or 594 nm stimulation light pulses wereindependently controlled.

Setup for concurrent acquisition of isosbestic control. For measurementsof GCaMP6 emission, both a 405 nm LED and a 470 nm LED (Thorlabs, M405F1and M470F1) were used as excitation sources for the calcium-dependentand calcium-independent isosbestic control measurements, respectively.The two LEDs were filtered with a 410-10 nm and 470-10 nm 1″ Ø bandpassfilters (Thorlabs, FB410-10 and FB470-10), fiber coupled as describedabove, combined using a 425 nm longpass dichroic mirror (Thorlabs,DMLP425R) and coupled into the microscope using a 495 nm longpassdichroic mirror (Semrock, FF495-Di02-25×36).

Dual-color recording setup. To enable simultaneous GCaMP6 and R-CaMP2recording, the 535 nm bandpass emission filter was removed and an imagesplitter (Photometrics, DualView-Lambda®) was introduced in between thecamera and the tube lens, enabling us to record the GCaMP6 and R-CaMP2emission onto separate halves of the same camera sensor. Inside theimage splitter, a 555 nm dichroic mirror (Semrock, FF555-Di03-25×36)separates the emission into two channels, each of which are additionallyfiltered by a 600-37 nm (Semrock, FF01-600/37-25) and 520-35 nm emissionfilters (Semrock, FF01-520/35-25), respectively, and then projected ontothe camera sensor. An additional dichroic cube allowed us to incorporatea 565 nm LED (Thorlabs, M565F1) for R-CaMP2 excitation with a 560-14 nmexcitation filter (Semrock, FF01-560/14-25), in conjunction with the 410nm and 470 nm LEDs as described previously for GCaMP6 recording. Each ofthe three LEDs was coupled via a 1000 μm Ø, 0.48 NA fiber (Thorlabs) toeither a 405 nm f=4.02 mm, 0.6 NA collimator (410 nm and 470 nm LED;Thorlabs, F671SMA-405 and AD11F) or a 543 nm f=4.34 NA collimator (560nm LED; Thorlabs, F230SMA-A). The 410 nm and 470 nm output from thecollimators were first combined with a 425 nm longpass dichroic mirror(Thorlabs, DMLP425R), and then combined with the 560 nm light using asecond 520 nm dichroic, (Semrock, FF520-Di02-25×36), before finallybeing coupled into the microscope using a third multi-band dichroic(Semrock, FF410/504/582/669-Di01-25×36).

Setup for simultaneous recording and stimulation. For combined imagingand optogenetic stimulation, the 565 nm LED used for dual-colorrecording was replaced with a 594 nm laser (Cobolt, Mambo 100 mW). The594 nm laser was filtered with a 590-10 nm bandpass filter (ThorlabsFB590-10). An additional 525-39 nm green fluorescent protein (GFP)emission filter (Semrock, FF01-525/39-25) was placed in front of thetube lens, along with a 594 nm notch filter (Semrock, NF03-594E-25) tominimize direct laser emission detected by the camera. A multi-banddichroic (Semrock, Di01-R405/488/594-25×36) was used to reflect 470 nmand 594 nm excitation light into the back of the 20× objective. Ahigh-speed shutter (Stanford Research Systems, SR474) was placed infront of the laser to modulate the emission in synchrony with the otherLEDs and camera.

For 470 nm cross-stimulation experiments, to enable the delivery of 470nm excitation light at two different power levels, the 594 nm laser wasreplaced with another 470 nm LED, and the dichroic combining the 470 nmand 594 nm light was replaced with a 50:50 beamsplitter. During thecross-stimulation experiments, one 470 nm LED was set to a lower powerand activated for every camera exposure, while the other 470 nm LED wasset to a similar or higher power and activated only during thestimulation periods.

Setup for sCMOS and lock-in amplifier photoreceiver comparison. In orderto precisely replicate the previous photoreceiver lock-in detectionapproach, an optical chopping wheel was introduced after the collimated470 nm LED (Thorlabs, MC1510 and MC2000), and coupled it to themicroscope via a 200 μm Ø, 0.39 NA fiber (Thorlabs, M75L01) and a 543nm, f=7.86 mm, 0.51 NA collimator (Thorlabs, F240FC-A and AD12F) toilluminate only the center˜254 μm Ø region of the 400 μm Ø patchcord(˜10 mm (objective focal length)÷7.86 mm×200 μm). This alignment wasachieved by positioning the collimator using a 5-axis kinematic mount(Thorlabs, K5X1) and using the camera to visualize both the 400 μm Øimaging patchcord, and the size of the excitation spot from the 200 μm Øfiber-coupled LED using a fluorescent slide (Chroma, 92001) mounted atthe working distance of the objective. For this experiment, the 470 nmLED was the only excitation light source used with a 470 nm 1″ Øbandpass filter (Thorlabs, FB470-10) and a 495 nm longpass dichroicmirror (Semrock, FF495-Di02-25×36). Lastly, the signal from the opticalchopping wheel was synchronized to a lock-in amplifier (StanfordResearch, SR810 DSP), the output of which was sampled and digitized at10 kHz using data acquisition hardware (National Instruments, NIPCIe-6343-X).

Image Acquisition Using MATLAB®

Though the technique described here could be implemented using thestandalone image acquisition software for the sCMOS camera and digitalfunction generators to control the light sources, custom MATLAB®software was used to control all hardware and streamline dataacquisition. All software ran on a Dell T5600 computer running Windows®7 (64-bit). A custom Matlab® graphical user interface (GUI) controlledboth the sCMOS camera through the MATLAB® Image Acquisition Toolbox andthe LED light sources through a data acquisition hardware (DAQ)(National Instruments, NI PCIe-6343-X) and the MATLAB® Data AcquisitionToolBox. To minimize raw data volume for real-time applications, thecamera was set to 4-by-4 pixel binning and semi-automatically located asubregion containing only each of the fiber ends from which to acquiredata. Using this software, the 7 fiber signals from the raw camera framecan be calculated within ˜2-3 ms (measured when collecting both calciumand isosbestic signals at 40 Hz, and given the computer'sconfigurations). Separate scripts for each experiment generated digitalcontrol signals to operate any mouse behavior peripheral hardware. TheGUI software and example behavior control scripts are available athttps(colon)//github(dot)com/deisseroth-lab/multifiber.

Head-Fixed Apparatus and Stimulus Delivery

Except for during the freely moving 7-fiber recordings, mice werehead-fixed above an animal running wheel (Ware, Small 6″ wheel) using acustom machined head-plate holder. Custom-written Matlab® scriptsdelivered digital control signals to trigger water rewards and tailshocks synchronized to the camera imaging. Water rewards were deliveredthrough a small animal feeding tube (Popper and Sons, 16 gauge)connected to a normally-closed solenoid (Valcor, SV74P61T-1). Thesolenoid was powered by a 12V DC battery, and the power was gated by ametal-oxide-semiconductor field-effect transistor (MOSFET) (MouserElectronics). The solenoid was opened for 0.25-0.5 s, which resulted inwater droplets a few 10 s of μL in size. Tail shocks were administeredusing a stimulus isolator (WPI, Isostim A320R). The positive andnegative leads of the isolator were connected by lead wires (RoscoeMedical, WW3005) to two pre-gelled electrodes (Sonic Technology) thatwere attached to the mouse's tail.

Analysis

All analysis was performed using custom-written scripts in MATLAB®.Regions of interest (ROIs) were first manually drawn around the fiber(s)based on a mean image of the movie. The average fluorescence intensitywas calculated for each fiber. A “dark frame” image was acquired bytaking a movie with the patchcord attached to the mouse, but with noLEDs on. This offset value accounts for extraneous,non-genetically-encoded calcium indicator (GECI) related lightcontributing to the signal. This offset was subtracted from thefluorescence intensity for each fiber, and then the fluorescence timeseries was thresholded to remove large transients. A double exponentialwas then fit to the fluorescence time series, and the best fit wassubtracted in order to account for slow bleaching artifacts. A singlebaseline fluorescence value was calculated, either as the median of theentire trace (which robustly estimated the baseline fluorescence), or bymanually defining the baseline during visually-identified periods ofrest. The normalized change in fluorescence (dF/F) was calculated bysubtracting the baseline fluorescence from the fiber fluorescence ateach time point, and dividing this value by the baseline fluorescence.For 7-fiber experiments, the dF/F was further normalized by the maximumvalue for each fiber. For analysis shown in FIGS. 1C-1E, the 410 nmreference trace was scaled to best fit the 470 nm signal usingleast-squares regression. The scaled 410 nm reference trace was thensubtracted from the 470 nm signal to obtain the motion-corrected 470 nmsignal. Other than the plots shown in FIG. 1B for the 7-fiber imaging,no additional smoothing or filtering was applied to fluorescencemeasurements. For FIG. 1B, a 1 s average sliding window was applied tothe traces. To calculate correlation coefficients, MATLAB®'S “con”function was used. To ensure that the increase in correlation during thesocial interactions was significantly greater than what one would expectfrom merely increased activity, each fiber's trace was circularlypermuted 1,000 times using a random shift between 0 and 5 minutes. Foreach shuffle, the pooled mean r value was calculated across all mice andunique brain region pairs. A p-value<0.001 means that none of the mean rvalues calculated from the 1,000 shuffled traces were greater than theactual calculated mean r value.

Experimental Parameters

sCMOS and lock-in amplifier photoreceiver experiments. Mice were waterdeprived to ˜80% of their starting weight. Head-fixed mice were trainedto lick water rewards that were delivered through an animal feedingneedle. Water rewards were given as a 0.25 s opening of the solenoid,and delivered at 10 s intervals. The SNR was calculated as the peak dF/Fdivided by the standard deviation of the baseline dF/F. Here, the peakdF/F was the maximum value during the first 2 s of reward, and thebaseline dF/F was measured during the period 0.5 s prior to rewarddelivery. Only a single fiber was implanted in the VTA. A low imagingpower of 2.5 μW (measured at the face of a 400 μm Ø patchcord) was used.For imaging parameters, see Example 6.

Multi-fiber experiments. For the 7-fiber experiment, the branchingpatchcord was coupled to the ferrules implanted in the mouse withceramic sleeves. The mouse was allowed to freely navigate its cage andsocialize with a novel mouse (of the same gender and age) while calciumsignals were recorded. For 7-fiber experiments, alternating frames withexcitation wavelengths of 470 nm and 410 nm were imaged at 40 Hz,resulting in frame rates of 20 Hz for both the GCaMP6 calcium andisosbestic control signals. For the 4-fiber experiments, mice werewater-deprived and administered either water rewards or tail shockswhile head-fixed and running on a wheel. Water rewards were given as a0.5 s opening of the solenoid, and tail shock were given as 450 mspulses spaced 5 ms apart for 2 s (4 shocks at 0.5 Hz). Water rewards andshocks were given at 10 s intervals. The response size to reward orshock was defined as the difference between the mean stimulus dF/Fduring the first 1 s of the reward or shock, and the mean baseline dF/Fduring the 2 s prior to the reward or shock. For 4-fiber experiments,alternating pulses with excitation wavelengths of 470 nm and 410 nm wereimaged at 20 Hz, resulting in frame rates of 10 Hz for both the GCaMP6calcium and isosbestic control signals. Typically 10-20 μW of 470 nmimaging light power was used, and 410 nm LED light power was adjusted toapproximately match the GCaMP6 fluorescence emission produced by the 470nm imaging light.

Dual-color experiments. Mice were water-deprived and administered eitherwater rewards or tail shocks while head-fixed using the same parametersas in the multi-fiber experiments. Response sizes to reward or shockwere calculated as described for the multi-fiber experiments.Alternating pulses of simultaneous 470 nm and 560 nm light, and 410 nmlight, were imaged at 20 Hz, resulting in frame rates of 10 Hz forGCaMP6 and R-CaMP2, and for the control signals. 10-20 μW of 470 nm and560 nm imaging light power was used, and the 410 nm LED light power wasadjusted to approximately match the GCaMP6 and R-CaMP2 fluorescenceemission produced by the 470 nm and 560 nm imaging light.

Combined imaging and stimulation experiments. Mice were water-deprivedand administered either optogenetic stimulation or water rewards whilehead-fixed using the same parameters as in the multi-fiber experiments.The response size to optogenetic stimulation or reward was defined asthe difference between the mean stimulus dF/F during the first 0.5 s ofthe light or reward, and the mean baseline dF/F during the 0.5 s priorto the light or reward. To sample calcium signals at 20 Hz, 470 nmexcitation pulses that were 12.5 ms in length and spaced 50 ms apartwere used for a 25% duty cycle. The camera exposed frames only duringeach 470 nm excitation pulse, resulting in 25% duty cycle imaging.Additional 470 nm or 594 nm stimulation pulses were delivered in betweenthe 470 nm imaging excitation pulses, at a rate of 20 Hz for 0.5 s (10pulses with 12.5 ms pulse width for a 25% duty cycle). Though longerexposure times could have been used to increase the amount of signalrecorded, a larger separation between the stimulation periods and thecamera exposure times was chosen, so that there was no question aboutwhether signal artifacts were being measured, where the 470 nm or 594 nmstimulation pulses contributed additional excitation of GCaMP6 within acamera exposure. A 410 nm isosbestic GCaMP control signal was notrecorded for these experiments. Identical light powers for the 470 nmimaging and stimulation pulses for the 5 μW and 10 μW experiments wereused. However, for the 50 μW and 220 μW 470 nm stimulation pulses, theimaging 470 nm LED was kept at 10 μW to avoid unnecessary bleaching ofthe GCaMP6 fluorescence, and the additional stimulation 470 nm LED wasset to 50 or 220 μW. For all 594 nm stimulation pulses and water rewardmeasurements, the imaging 470 nm LED was kept at 5 μW. For the controlmouse, GCaMP6 fluorescence was recorded with 20 μW pulses of 470 nmimaging light, and identical 20 μW pulses of 470 nm stimulation lightand 0.5 mW pulses of 594 nm stimulation light. GCaMP6 fluorescence with50 μW pulses of 470 nm imaging light, and identical 50 μW pulses of 470nm simulation light and 0.5 mW pulses of 594 nm stimulation light, werealso recorded.

Cultured Neuron Intracellular Patching and Imaging for GECI IsosbesticWavelengths

Dissociated rat hippocampal neurons were cultured and transfected withboth GCaMP6m and R-CaMP2 as previously described. Coverslips of culturedneurons were transferred from the culture medium to a recording bathfilled with Tyrode's solution (containing in mM: 125 NaCl, 2 KCl, 2CaCl₂, 2 MgCl₂, 30 glucose, 25 HEPES). Whole-cell patch clamp recordingswere performed on healthy GECI-expressing neurons at room temperature.Resistance of the glass patch pipettes was 3-4 MS2 (Sutter Instruments,P-2000) when filled with intracellular solution containing the following(in mM): 150 K-gluconate, 5 NaCl, 1 MgCl₂, 0.2 EGTA, 10 HEPES, 2 Mg-ATP,0.3 Na-GTP, adjusted to pH 7.3 with KOH. Signals were amplified with aMulticlamp 700B amplifier, and acquired using a DigiData 1440A digitizersampled at 10 kHz and filtered at 2 kHz (Molecular Devices). Allelectrophysiological data acquisition was performed using pCLAMPsoftware (Molecular Devices). Imaging was performed using a 40×/0.8 NAobjective (Olympus), Rolera XR camera (Q-Imaging), and Spectra X Lightexcitation source (Lumencor), all coupled to an Olympus BX51 WImicroscope. The following bandpass filters were used with the Lumencorfor excitation wavelengths: 405-10 nm (Thorlabs, FB405-10), 470-10 nm(Thorlabs, FB470-10), and 560-10 nm (Thorlabs, FB560-10). GCaMP6memission was reflected off a 495 dichroic mirror (Semrock,FF495-Di03-25×36) and passed through a 535-30 nm emission filter(Chroma, ET535/30m), and R-CaMP2 fluorescence was reflected off a 585 nmdichroic (Chroma, T585LP) and passed through a 630-75 nm emission filter(Chroma, ET630/75m). Images were acquired at 10 Hz using QCapture Pro7Software (Q-imaging). While synchronously measuring GCaMP6m or R-CaMP2fluorescence from a neuron, action potentials were driven by injectingbrief current pulses (5 ms, 1-2 nA) at 10 Hz for 3 s (resulting in 30action potentials). The response size to the stimulation train wasdefined as the difference between the mean stimulus dF/F during thefirst 3 s of the stimulation train, and the mean baseline dF/F duringthe 3 s prior to the stimulation train.

bReaCh-ES Design and Characterization

bReaCh-ES was generated by introducing a Glu123Ser mutation in thepreviously published ReaChR construct (see also, Example 8). Dissociatedrat hippocampal neurons were cultured and transfected with either ReaChRor bReaCh-ES. The same intracellular recording procedures were used asfor the GECI isosbestic cultured neuron intracellular recordings. Actionpotentials were elicited with a 4 s pulse train of 590 nm light (5 mspulse width) delivered at various frequencies, using a Spectra X Lightsource and 590-10 nm excitation filter (Thorlabs). Steady-state currentand tau-off kinetics were measured using a constant illumination of 4 s.

Animal Surgical Procedures and Viruses

All experimental and surgical protocols were approved by StanfordUniversity's Institutional Animal Care and Use Committee. For allsurgeries, stainless steel headplates and ferrules were fixed to theskull using Metabond (Parkell). Mice were anesthetized with 1.5-2.0%isoflurane and were placed on a heating pad in a stereotaxic apparatus(Kopf Instruments). All viruses were produced at the Stanford Viral andVector Core—GVVC (Stanford University).

For the 7-fiber surgery, DAT::Cre B6.SJL-S1c6a3tm1.1(cre)Bkmn/J (JAX®stock 006660) male or female transgenic mice were stereotaxicallyinjected as previously described with 1000 nL of AAVDJ-CaMKIIα-GCaMP6f(2.7e12 vg/ml) at six locations: PFC, A/P+2.2, M/L +0.35, D/V −2.2; NAc,A/P +1.15, M/L −1.65, D/V −4.2; BLA, A/P −1.54, M/L −3.0, D/V −4.6; LH,A/P −0.9, A/P −1.1, D/V −5.0; BNST, A/P +0.9, M/L +0.1, D/V −4.4; andCA1, A/P −1.75, M/L +1.5, D/V −1.25. Mice were injected with 1000 nL ofAAVDJ-EF1α-DIO-GCaMP6f (1.5e13 vg/ml) in the VTA: A/P −3.1, M/L −0.4,D/V −4.4. Custom 400 μm Ø 0.48 NA fibers attached to a 1.25 mm Østainless steel ferrule (Doric Lenses) were stereotaxically implanted atthe same seven coordinates.

For 4 fiber surgeries, DAT::Cre male or female transgenic mice wereused. Mice were stereotaxically injected as previously described with1000 nL of AAVDJ-EF1α-DIO-GCaMP6f (1.5e13 vg/ml) at two locations in theVTA: A/P −3.3, M/L −0.3 and −0.5, D/V −4.2. Custom 400 μm Ø 0.48 NAfibers attached to a 1.25 mm Ø stainless steel ferrule (Doric Lenses)were stereotaxically implanted at 4 locations: VTA, A/P −3.3, M/L −0.4,D/V −4.2; PFC, A/P +2.2, M/L −0.35, D/V −2.0; NAc, A/P +1.2, M/L −1.75,D/V −4.0; and BLA, A/P −1.54, M/L −2.8, D/V −4.5.

For dual-color R-CaMP2 and GCaMP6 imaging, 1000 nL of a 1:1 mixture ofAAVDJ-hSyn-DO-GCaMP6m (2.9e12 vg/ml) and AAVDJ-EF1α-DIO-RCaMP2 (8.0e12vg/ml) was injected into the VTA at A/P −3.3, M/L −0.4, D/V −4.2. Acustom 400 μm Ø 0.48NA fiber attached to a 1.25 mm Ø stainless steelferrule was implanted at the same location.

For GCaMP6 imaging and bReaCh-ES stimulation, 1000 nL of a 1:1 mixtureof AAVDJ-EF1α-DIO-GCaMP6f (1.5e13 vg/ml) andAAVDJ-EF1α-DIO-bReaCh-ES-TS-mCherry (5.8e12 vg/ml) was injected into theVTA of a DAT::Cre mouse at A/P −3.3, M/L −0.4, D/V −4.2. A custom 400 μmØ 0.48 NA fiber attached to a 1.25 mm Ø stainless steel ferrule wasimplanted at the same location. As a control, a DAT::Cre mouse wasinjected with 1000 nL of a 1:1 mixture of AAVDJ-EF1α-DIO-GCaMP6f (5.8e12vg/ml) and AAV8-EF1α-DIO-mCherry (1.7e13 vg/ml) into the VTA, andimplanted with a 400 μm Ø 0.48 NA fiber at the same coordinates.

Histology

Mice were heavily anesthetized with isoflurane, and then perfused with20 mL of cold phosphate buffered saline (PBS) followed by 20 mL of coldparaformaldehyde (PFA). The brain was extracted from the skull and keptin PFA for 24 hours, and then transferred to a 30% sucrose solution.After 48 hours, the brains were sliced into 50-100 μm thick sectionsusing a vibratome (Leica VT1200S) in cold PBS. Slices were then washedin PBS at room temperature 3 times for 5 minutes each. For GCaMP6 andtyrosine hydroxylase (TH) staining, slices were incubated in a blockingsolution of PBS+0.3% Triton®-X (polyethylene glycolp-(1,1,3,3-tetramethylbutyl)-phenyl ether) (PBST) with 5% normal donkeyserum (NDS) for 1 hour. Slices were then incubated for 24 hours at 4° C.in PBST+NDS blocking solution containing a primary rabbit antibodyagainst GFP conjugated to Alexa®488 (Life Technologies, A21311, 1:500)and a primary chicken antibody against TH (Ayes Lab, 1:500). Slices werewashed 3 times for 10 minutes in PBST, and incubated in blockingsolution containing a donkey anti-chicken Alexa® 647 secondary antibody(Millipore, AP194SA6) for 2 hours at room temperature. Slices werewashed with PBST 3 times for 10 minutes each, and finally stained for(4′,6-diamidino-2-phenylindole) DAPI (1:1000) for 10 minutes and mountedonto glass slides. For the TH staining in the dual-color mouse, normalgoat serum (NGS) was used instead of NDS, and no Triton®-X (polyethyleneglycol p-(1,1,3,3-tetramethylbutyl)-phenyl ether) was added at any step.The same TH antibody was used with a goat anti-chicken Alexa®647secondary antibody (Life Technologies, A21449, 1:500). No DAPI orprimary antibodies against GCaMP6 or R-CaMP2 were used.

Example 2: System Design, Alignment, and Calibration Considerations forFIP Microscopy

A basic microscope consisting of the objective lens and tube lens wasconstructed, where the sCMOS camera was focused on the fiber(s) mountedat the working distance of the objective (FIG. 1A). Here, the objectiveand tube lens were chosen to set the magnification of the fibers ontothe sensor, which determines the number of pixels on the camera that agiven fiber tip is imaged onto. Note that the objective field of viewand NA is larger than the fiber size and NA. Given that the dominantnoise source of the sCMOS camera is read noise, the image may be sampledwith as few sCMOS pixels as possible without saturating any pixels.However, for low light levels, photon shot noise may dominate the readnoise, in which case more excitation light power may be used to generatemore emission photons, and more camera pixels may be used to sample theemission without saturating. The excitation light sources were thenadded using dichroic mirrors between the tube lens and the objective.Similar to the tube lens of the camera, the focal length of thecollimators for each excitation light source was chosen to set themagnification and NA to correctly fill the fiber(s). To align therelayed image of each excitation light source onto the previouslyaligned fiber(s), the position of the fiber(s) was annotated in thecamera view and the excitation light sources were each positioned to becentered over the fiber(s) (FIG. 3A). Finally, in the dual-color imagingexperiments with the image splitter, the image splitter was simplyattached to the camera and positioned until the now two images of thefiber(s) were in focus again. The synchronization of the light sourcesto the sCMOS camera was tested using a fluorescent slide. The duty cycleand precise on-time of each light source was adjusted to accommodate thecamera's rolling shutter and the off-slew-rate of each light source.This timing adjustment can be done once for each light source for eachset of digital control waveforms.

Example 3: Simultaneous Calcium Measurements from Multiple Deep BrainRegions Using an sCMOS Camera

To develop FIP microscopy, in vivo GCaMP6 recordings obtained with ansCMOS camera was compared to those obtained with a previously publisheddesign involving a photoreceiver and lock-in amplifier. The camera setupwas modified to direct half the fluorescence emission from a singlefiber onto a photoreceiver using a beamsplitter; excitation light wasmodulated for lock-in detection as previously described. The sCMOScamera measurement (even without lock-in detection) was found to be atleast as sensitive as the measurement using a photoreceiver and lock-inamplifier (see Example 6; FIGS. 3A-3C).

The beamsplitter and photoreceiver was then removed to collect all fiberemissions onto the camera sensor. To control for non-Ca²⁺ relatedfluorescence changes due to brain motion or fiber bending, camera framescorresponding to excitation of GCaMP6 and R-CaMP2 near their respectiveoptical Ca²⁺-dependent excitation wavelengths (470 nm or 560 nm), andalso near the isosbestic wavelength (410 nm) were alternately acquired.Using simultaneous imaging paired with intracellular currentinjection-driven defined spiking patterns in cultured neurons, it wasconfirmed that GCaMP6 and R-CaMP2 increased fluorescence emission inresponse to action potentials when excited at 470 nm and 560 nmrespectively, but exhibited virtually no change in emitted fluorescencewhen excited near 410 nm (see Example 7; FIGS. 4A-4F). Thus any changesobserved while imaging either GCaMP6 or R-CaMP2 with 410 nm light werelikely due to either motion-related artifacts or changes in intrinsicsignals unrelated to neural activity. The ability to simultaneouslyrecord both the calcium-dependent signal and the 410 nm control signalallowed identification of artifacts that contaminate the signal inreal-time, rather than in separate fluorophore-only cohorts. It wasconfirmed that large motion artifacts could be detected and correctedfor in vivo when imaging GCaMP6 simultaneously with 470 nm and 410 nmlight (FIG. 5).

FIG. 5. Example of correcting motion-related artifacts present in the410 nm isosbestic wavelength. Example of simultaneously recorded GCaMP6signals using 470 nm and 410 nm excitation (left traces). The 410 nmsignal has been scaled using least-squares regression to minimize thedifference between the 410 and 470 nm signal. The scaled 410 nm tracefrom the 470 nm trace was then subtracted to generate the corrected 470nm signal (right trace).

The FIP microscope's ability to simultaneously record GCaMP6 Ca²⁺signals from multiple fibers in vivo was then tested. A 7-fiberpatchcord tightly bundled on one end and split into 7 separate brancheson the other was used, to both deliver excitation light and collectemission light. Each of these 7 branches was coupled to a fiberopticinterface implanted into different widely-dispersed regions in an adultmouse; a single fast sCMOS camera then was interfaced to the output end,simultaneously measuring fluorescence emission from all 7 fibers byimaging the tightly bundled end of the patchcord (FIG. 1A). Using theFIP microscope, simultaneous and temporally registered GCaMP6f signalsacross the brain in a freely moving mouse was then measured. Thetargeted areas were 1) bed nucleus of the stria terminalis (BNST), 2)nucleus accumbens (NAc), 3) ventral tegmental area (VTA), 4) lateralhypothalamus (LH), 5) basolateral amygdala (BLA), 6) hippocampal regionCA1, and 7) prefrontal cortex (PFC) in DAT::Cre driver mice. ACre-dependent GCaMP6f virus was injected into the VTA to preferentiallylabel dopamine (DA) neurons, while a CaMKIIα-GCaMP6f virus was injectedin the other regions. GCaMP6f fluorescence signals that were presentwith 470 nm excitation, but absent with isosbestic-range 410 nmexcitation (FIG. 1B) where only small, non-Ca²⁺ dependent changes(likely due to motion or system-related artifacts; for example in CA1)were observed. The 470 nm signals were then normalized by the 410 nmcontrol traces, and neural activity was measured across all 7 brainregions during naturalistic and freely-moving social interactions.Spontaneous activity could be robustly observed in all 7 brain regions,in addition to a time-locked increase in fluorescence activity upon theintroduction of a novel mouse (FIG. 1C). Joint-statistical relationshipamong the brain regions was calculated using Pearson's correlationduring periods when the mouse was alone versus when the mouse wassocializing (FIG. 1D), and a global increase in pair-wise correlationsacross brain regions was observed when the mouse was socializing with anovel mouse (FIG. 1D). Shuffling analysis confirmed that this increasein pair-wise correlations was significantly greater than what wouldexpected from simply increased activity in all of these regions(p<0.001, out of 1,000 shuffles).

FIG. 1. Simultaneous calcium measurements from multiple deep brainregions using an sCMOS camera. FIG. 1A) Schematic of microscope forsimultaneous FIP calcium recordings. An example image of the bundledfiber faces is shown in the upper right inset. The lower left insetillustrates the time-division multiplexing scheme for simultaneouslyimaging GCaMP6 with 470 nm and 410 nm. FIG. 1B) Left: example image of amouse implanted with 400 μm fibers in 7 different regions expressingGCaMP6f. Center: example calcium traces recorded from a freely movingmouse. Right: simultaneously recorded control traces. FIG. 1C) ExampleGCaMP6f fluorescence traces simultaneously acquired across the 7different brain regions listed in FIG. 1B) when the mouse was aloneversus when the mouse was placed with a novel mouse. The total imagingtime was 10 min for each condition. Traces are plotted as dF/Fnormalized to each trace's maximum value. FIG. 1D) Top: Heat maps of thePearson's correlation coefficients (r) calculated between all 7 brainregions for the example mouse shown in FIG. 1C). Bottom: Spatialrepresentations of the Pearson's correlation coefficients between eachbrain region. Brain regions are plotted according to theanterior/posterior and medial/lateral coordinates where the fibers wereimplanted. The thickness of the lines connecting each brain regionrepresents the magnitude of r. FIG. 1E) Summary of the mean r valuesbetween all brain regions calculated when the mouse was alone versus inthe presence of a novel mouse. The mean r value significantly increasedin the presence of a novel mouse compared to the baseline alone value(0.31±0.024 versus 0.43±0.024, p<0.001, n=84 pairs from 4 mice,Wilcoxon's rank-sum test). FIG. 1F) Schematic of surgery and recordingsetup for 4-fiber experiment. FIG. 1G) Example GCaMP6f fluorescencetraces simultaneously acquired in each brain region in response toreward and tail shock. Solid lines denote calcium transients, dashedlines denote control signal (mean±S.E.M.; n=6 trials from one mouse).FIG. 1H) Summary of the mean responses to reward and shock in each brainregion (dF/F_(stimulus)−dF/F_(baseline)). Asterisks indicate significantresponse (p<0.05, n=6 trials, Wilcoxon's signed-rank test).

The sensitivity limits of the system were next tested by recording Ca²⁺signals not only from populations of cell bodies, but also from axonalprojections to multiple independent regions. Here, a single injection ofCre-dependent GCaMP6f was made into the VTA of DAT::Cre driver mice.Optical fibers were then implanted in PFC, NAc, BLA, and VTA tosimultaneously record from VTA-DA cell bodies or their axonal terminalsin these downstream regions with the FIP microscope while administeringcontrolled, time-locked water rewards or aversive tail shocks (FIG. 1F).It was found that the VTA-DA cell bodies exhibited increased activityduring the rewarding stimulus, and decreased activity in response to theaversive tail shock, consistent with previous recordings from VTA-DAneurons. In contrast, the VTA-DA→BLA projection increased activity inresponse to both the reward and the tail shock. The VTA-DA→NAcprojection showed a similar pattern compared with the VTA-DA cell bodies(increased activity in response to reward and decreased in response totail shock), but activity in the VTA-DA→PFC projection exhibited yet athird pattern (increased response to tail shock but not reward; FIG. 1G,solid dark green). Supporting validity of the FIP approach, theseresults were consistent with previous studies that individually andseparately tracked activity in different populations of VTA-DA neuronsencoding rewarding or aversive stimuli depending on their projectiontarget (though without the joint simultaneity of FIP during behavior).

Response sizes are summarized in FIG. 1H; as expected, there was littlechange in the GCaMP6f control signal measured at 410 nm (FIG. 1G, dashedlight green). Raw GCaMP6f fluorescence traces are shown in FIGS. 6A-6B,and mean changes for the control signals are plotted in FIG. 6C (allinsignificant). Table 1 summarizes the significant GCaMP6f responsesrecorded during reward and shock (with insignificant changes in GCaMP6fisosbestic control fluorescence). Histology confirming locations offibers and expression of GCaMP6f in cell bodies and terminals isprovided in FIGS. 7A-7D. Note that very sparse GCaMP6f fibers localizedto the amygdala regions surrounding the BLA was observed, and thesefibers could also be contributing to the signal.

TABLE 1 Number of mice showing significant GCaMP responses to reward ortail shock with 470 nm light for 4-fiber experiment. Brain Region RewardTail Shock VTA-DA in PFC N.S. 3 mice VTA-DA in NAc 7 mice 4 mice VTA-DAin BLA 3 mice 2 mice VTA-DA 6 mice 5 mice p < 0.05, Wilcoxon'ssigned-rank test, n = 6-12 trials for each mouse. p > 0.05 for controlGCaMP6 responses with 410 nm light for all mice.

Example 4: Dual Color Imaging of Different Populations

The FIP microscope was readily adaptable for dual-color imaging ofdifferent populations using two different Ca²⁺ sensors (in this caseGCaMP6 and R-CaMP2). By placing an image splitter in front of the camerasensor and adding an additional 560 nm excitation source (FIG. 8A), itwas possible to simultaneously collect GCaMP6 and R-CaMP2 fluorescenceemission through the same fiber. VTA-DA expressing and VTA-non-DAexpressing neurons in DAT::Cre mice was labeled using a Cre-activated(DIO) AAV:R-CaMP2 virus and a Cre-deactivated (DO) GCaMP6m virus,respectively (FIG. 2A). This viral strategy resulted in labeling oflargely non-overlapping populations of R-CaMP2 and GCaMP6m neurons inthe VTA (FIG. 2B), and expression of DIO:R-CaMP2 was found toco-localize with the tyrosine hydroxylase (TH) stain for DA-expressingneurons (FIGS. 9A-9B). While monitoring these neural populations withthe FIP microscope, reward or tail shock stimuli was administered.Consistent with the earlier 4-fiber recordings, it was found thatactivity in VTA-DA neurons significantly increased in response to rewardand significantly decreased in response to tail shock (FIG. 2C-2D). Itwas found that the VTA non-DA neurons exhibited a significant increasein fluorescence in response to both reward and tail shock (FIG. 2C-2D),consistent with previous electrical recordings. There was no significantchange in R-CaMP2 or GCaMP6m control fluorescence in response to 410 nmexcitation during reward or tail shock (FIG. 2C).

FIGS. 2A-2D. Dual-color imaging of different populations. FIG. 2A)Schematic of dual-color imaging surgery preparation. FIG. 2B)Non-overlapping populations of VTA-DA neurons and VTA-non-DA labeledwith R-CaMP2 and GCaMP6m, respectively. Scale bar indicates 25 μm. FIG.2C) VTA-DA and VTA-non-DA fluorescence traces in response to reward andtail shock (red, VTA-DA neurons; green, VTA-non-DA neurons; solidcurves, calcium transients; dashed curves, control signals). FIG. 2D)Summary of the mean responses to reward and shock(dF/F_(stimulus)−dF/F_(baseline)). VTA-DA neural activity increased inresponse to reward (5.39±0.32% dF/F) and decreased in response to shock(−1.18±0.45% dF/F), while VTA-non-DA neural activity increased inresponse to both reward (3.26±0.14% dF/F) and shock (2.08±0.14% dF/F).Asterisks indicate p<0.05, n=10 trials, Wilcoxon's signed-rank test.

FIG. 8A. Microscope configuration used for dual-color imagingexperiments. a) Schematic of setup for dual-color imaging. An imagesplitter was placed before the camera sensor, and an additional 560 nmLED was used to image R-CaMP2. The lower left inset represents thetime-division multiplexing strategy used to simultaneously image GCaMP6and R-CaMP2 at both their calcium sensitive and insensitive wavelengths.

FIGS. 7A-7B. Confirmation of fiber location and virus specificity fordual-color imaging. FIG. 7A) 10× magnification images of a slicecontaining VTA. GCaMP6m fluorescence in VTA-non-DA neurons is shown ingreen, R-CaMP2 fluorescence in VTA-DA neurons is shown in red, and a THstain is shown in white. Dashed white rectangle indicates fiberlocation. Scale bar indicates 100 μm. FIG. 7B) 63× magnification imagesof VTA slice with same staining. Bottom right image is a merge of allthree channels. Scale bar indicates 25 μm.

Example 5: Dual Color Imaging of Different Populations

The FIP microscope readily allowed tuning optogenetic stimulation tomatch activity levels that naturally occurred with behaviorally-relevanttiming within the very same targeted neural population at the samelocation in the same experimental subject (FIGS. 2E-2H). Simultaneousrecording and perturbation of neural activity was performed using GCaMP6and a potent and fast red-shifted channelrhodopsin, bReaCh-ES (Methods,Example 8, and FIGS. 10A-10F). The 560 nm LED used to image R-CaMP2 wasreplaced with a 594 nm laser for bReaCh-ES (FIG. 8B), andDIO-bReaCh-ES-TS-mCherry was virally expressed along with DIO-GCaMP6f inthe VTA of DAT::Cre mice in order to both image and perturb VTA-DAneurons (FIG. 2E), anticipating that the high light sensitivity of theFIP microscope could allow recording of GCaMP6f signals under very lowimaging power that would minimize cross-stimulation of bReaCh-ES byGCaMP6f excitation light (Example 9). GCaMP6f fluorescence responses tointerleaved pulses of 470 nm stimulation light identical to the 470 nmpulses used to image GCaMP6 was measured; GCaMP6f responses to 594 nmpulses, and to a naturalistic water reward were also measured (FIG. 2F).It was found that using 5 μW of power (measured at the face of the 400μm Ø patchcord, for 470 nm imaging and stimulation) resulted in minimalchanges in GCaMP6f fluorescence (FIG. 2G), while higher light powers of470 nm light elicited much larger GCaMP6f transients as a result ofopsin cross-stimulation (FIGS. 11A-11B). Using only 5 μW of 470 nmimaging light power was still sufficient to observe VTA-DA responses to594 nm bReaCh-ES stimulation that scaled with light intensity (FIG. 2G),and could be tuned to match amplitude of VTA-DA responses to waterreward in the very same animal (FIG. 2G). A summary of the mean GCaMP6fresponse size to various stimulation wavelengths and powers is shown inFIG. 2H. A control DAT::Cre mouse expressing DIO-GCaMP6f and DIO-mCherryexhibited no significant changes in GCaMP6f fluorescence in response tointerleaved 470 nm or 594 nm stimulation light, but did exhibit GCaMP6ftransients as expected during interaction with a novel mouse, known toelicit VTA-DA activity (FIGS. 11C-11D).

FIGS. 2E-2H. Simultaneous recording and perturbation of neural activity.FIG. 2E) Schematic of combined imaging and optogenetics surgerypreparation. FIG. 2F) Schematic of imaging paradigm. For experiments, 10stimulation pulses were used. FIG. 2G) Example GCaMP6f fluorescencetraces in response to bReaCh-ES cross-stimulation with with 5 μW of 470nm light (light blue), bReaCh-ES stimulation with 594 nm light (light todark orange denote 0.5 mW, 1 mW, and 2 mW of power), or a water reward(cyan). FIG. 2H) Summary of the mean responses to bReaCh-ES stimulationor reward (dF/F_(stimulus)−dF/F_(baseline)). The mean VTA-DA neuronresponse size to 5 μW 470 nm stimulation (n=6 trials, 2.27±0.57% dF/F)was significantly smaller than the response size to the reward (n=4trials, 8.27±1.63% dF/F, p<0.05, Wilcoxon's rank-sum test).

FIG. 8B. Microscope configurations used for simultaneous imaging andperturbation experiments. b) Schematic of setup for simultaneous imagingand perturbation experiments. The 560 nm LED was replaced with a 594 nmlaser for optogenetic stimulation. For cross-stimulation measurements,the 594 nm laser was replaced with an additional 470 nm LED, and thedichroic combining the 470 nm and 594 nm light was replaced with a 50:50beamsplitter.

FIGS. 10A-10F. Characterization of novel bReaCh-ES opsin. FIG. 10A)Example of internal current elicited by a 4 s pulse of 590 nm light(orange) for neurons expressing ReaChR or bReaCh-ES. FIG. 10B) Voltagerecordings showing 4 APs in response to 4, 5 ms pulses of 590 nm(orange) light delivered at 1 Hz to neurons expressing ReaChR orbReaCh-ES. FIG. 10C) Voltage recordings showing APs in response to 80, 5ms pulses of 590 nm light (orange) delivered at 20 Hz to neuronsexpressing ReaChR or bReaCh-ES. FIG. 10D) Average tau-off kineticsmeasured for ReaChR and bReaCh-ES. The mean tau-off for bReaCh-ES wassignificantly smaller than that of ReaChR (ReaChR: 531.83±40.29 ms;bReaCh-ES: 39.33±3.69 ms; p<0.005, n=6 cells, Wilcoxon's rank-sum test).FIG. 10E) Steady-state current measured for ReaChR and bReaCh-ES. Therewas no significant difference between steady-state current betweenReaChR and bReaCh-ES (ReaChR: 946.00±121.97 pA; bReaCh-ES: 941.17±169.30pA; p>0.05, n=6 cells, Wilcoxon's rank-sum test). FIG. 10F) Percentageof APs successfully elicited by a 4 s train of 590 nm light pulses (5 mspulse width) delivered at 1, 2, 5, 10, and 20 Hz to neurons expressingReaChR or bReaCh-ES. At 10 and 20 Hz, bReaCh-ES stimulation elicits asignificantly higher percentage of successful APs than ReaChR (ReaChR:12.08±9.58% at 10 Hz, 2.29±1.04% at 20 Hz; bReaCh-ES: 100±0% at 10 and20 Hz; p<0.005, n=6 cells, Wilcoxon's rank-sum test).

FIGS. 11A-11D. Control for simultaneous imaging and perturbationexperiment. FIG. 11A) Example GCaMP6f fluorescence traces in response tobReaCh-ES cross-stimulation with 470 nm light (light to dark bluerepresents 10 μW, 50 μW, and 220 μW of power). FIG. 11B) Summary of themean GCaMP6f responses to bReaCh-ES cross-stimulation with 470 nm light(dF/F_(stimulus)−dF/F_(baseline)). FIG. 11C) Top: Example GCaMP6ffluorescence trace taken from a control mouse expressing mCherry insteadof bReaCh-ES to demonstrate that there is functional GCaMP6f present.Bottom: GCaMP6f fluorescence traces in response to 0.5 mW 594 nmstimulation pulses (orange), and to 20 or 50 μW 470 nm stimulationpulses (blue). FIG. 11D) Summary of the mean GCaMP6f responses to light(dF/F_(stimulus)−dF/F_(baseline)) in the mCherry control mouse. Therewere no significant changes in GCaMP6f fluorescence with 470 nm or 594nm stimulation light (p>0.05 Wilcoxon's signed-rank test).

Example 6: Simultaneous Camera and Photoreceiver Lockin-In Measurements

To get a conservative estimate of how the sensitivity of the sCMOScamera without lock-in detection compares with the previousstate-of-the-art technique employing lock-in detection, an experimentwas conducted where the same calcium-dependent fluorescence was recordedsimultaneously with both techniques. To accomplish this, the excitationlight source was modulated at 448 Hz and synchronized with the lock-inamplifier configured with a −3 dB filter with 24 dB slope at 16 Hz(corresponding to 10 ms time constant), consistent with the imagingparameters described previously. Modulating the excitation source at 448Hz minimized both the presence of 60 Hz electrical noise in thephotoreceiver, and beating artifacts from the modulated light in thecamera. The emission from the fiber was equally split with abeamsplitter between the photoreceiver connected to the lock-inamplifier and the sCMOS camera. In order to match the 16 Hz bandwidthdetection of the lock-in amplifier, the camera was set to acquire framesat 32 Hz (to Nyquist sample the desired 16 Hz bandwidth). Importantly,while the signal from the lock-in amplifier benefits from thedemodulation of the 448 Hz carrier signal, no attempt was made todemodulate the signal recorded by the sCMOS camera though it would bepossible if sampling was done at a higher frame rate. Hence, the signalfrom the sCMOS camera was a conservative estimate of what would bemeasured with constant excitation without any modulation or lock-indetection.

Example 7: Isosbestic Excitation Wavelength of GCaMP6 and R-CaMP2

The published absorption spectrum of GCaMP3 and R-CaMP2 suggested thatan isosbestic point between 405-420 nm exists where the absolute GCaMPor R-CaMP emission is independent of calcium concentration. Previousstudies using the AM esterase dye Fura-2, for example, have usedfluorescence emission collected with the isosbestic excitationwavelength to measure calcium-independent changes in fluorescence of theindicator. Thus by simultaneously measuring the GCaMP6 and R-CaMP2fluorescence using the ˜isosbestic 410 nm wavelength, a reference signalcould be recorded that reported non-calcium related fluorescence changesthat could be contributing to the measured calcium signals. While boththe calcium signals and control signals were presented in the Examples,one could normalize the calcium signal by its corresponding controlsignal to estimate neural activity-related changes in fluorescence.

Example 8: Generation of bReaCh-ES Construct

Recently a red-shifted excitatory opsin, ReaChR, was published thatexhibits large photocurrents capable of transcranial optogeneticstimulation. However, photocurrents expressing ReaChR were accompaniedby a long tau-off, which hindered the ability to elicit APs atfrequencies higher than 1 Hz. A mutation to the existing ReaChR wasintroduced to generate bReaCh-ES, which exhibited the same largephotocurrents as ReaChR, but had a significantly short tau-off thatallows APs to be driven 100% reliably at up to 20 Hz (FIGS. 10A-10F).

Example 9: Procedure for Estimating Cross-Stimulation of bReaCh-ES

It is well known that the excitation spectrum of GCaMP6 and theexcitation spectrum of red-shifted indicators such as C1V1 exhibitsignificant overlap. As a result, a given choice of excitationwavelength for GCaMP6 may result in unwanted bReaCh-ES cross-stimulationto some extent, and this effect may be quantified. To characterize theamount of cross-stimulation of bReaCh-ES produced by the GCaMP6excitation light, additional pulses of 470 nm stimulation light at 20 Hz(10 pulses with 12.5 ms pulse width) were applied while imaging GCaMP6with 470 nm light (20 Hz, 12.5 ms pulse width). As expected, with higherpowers of the 470 nm blue excitation, larger changes in GCaMP6fluorescence were observed likely due to cross-stimulation of bReaCh-ES.As a comparison, the change in GCaMP6 fluorescence was also measured tointerleaved pulse trains of 594 nm light at 20 Hz (10 pulses with 12.5ms pulse width) intended to stimulate bReaCh-ES, and to a water reward.This protocol for characterizing the amount of cross-stimulation was amore explicit measure than those used in previous papers.

While the present disclosure has been described with reference to thespecific embodiments thereof, it should be understood by those skilledin the art that various changes may be made and equivalents may besubstituted without departing from the true spirit and scope of thepresent disclosure. In addition, many modifications may be made to adapta particular situation, material, composition of matter, process,process step or steps, to the objective, spirit and scope of the presentdisclosure. All such modifications are intended to be within the scopeof the claims appended hereto.

What is claimed is:
 1. A method comprising: a) illuminating a region ofa target tissue with a light stimulus comprising light pulses of aplurality of wavelengths, wherein: the region is labeled with one ormore cellular activity-dependent fluorescent moieties; and the lightpulses comprise: i) a first set of light pulses at a first wavelength;and ii) a second set of light pulses at one or more wavelengths, whereineach of the one or more wavelengths are different from the firstwavelength and are at an excitation wavelength of the one or morecellular activity-dependent fluorescent moieties, and wherein each lightpulse of the first set are interleaved among light pulses of the secondset, thereby generating fluorescence from the region, wherein amultimode optical fiber is configured to direct the light stimulus to,and collect the fluorescence from, the region; b) recording by an imagedetector, onto independent frames for each light pulse, an image of aterminal cross-section of the multimode optical fiber from the region,wherein a cross-sectional average of the fluorescence generated inresponse to the second set of light pulses is representative of anaggregate cellular activity of the region; and c) analyzing the recordedimage, to generate an output comprising a measure of the aggregatecellular activity in the region, wherein the analyzing comprises: 1)demarcating the cross-section of the multimode optical fiber from theregion in the recorded image; 2) calculating an average of thefluorescence across the cross-section; and 3) calculating a normalizedchange in the fluorescence over a baseline fluorescence for thecross-section of the multimode optical fiber in the recorded image,wherein the baseline fluorescence is a median of the averagefluorescence within the cross-section of the multimode optical fiberacross a plurality of recorded images.
 2. The method according to claim1, wherein the multimode optical fiber has a diameter in the range of100 to 1000 μm and the image detector comprises an image sensor.
 3. Themethod according to claim 1, wherein the region comprises one or morecollections of a plurality of neurons, or a subcellular portion thereoflabeled with one or more cellular activity-dependent fluorescentmoieties and the one or more collections comprise one or morefunctionally-defined collections of a plurality of neurons.
 4. Themethod according to claim 3, wherein the region comprises: a firstcollection of the plurality of neurons, each neuron of the firstcollection comprising a first cellular activity-dependent fluorescentmoiety; and a second collection of the plurality of neurons, each neuronof the second collection comprising a second cellular activity-dependentfluorescent moiety, and wherein the second set of light pulses comprise:a third set of light pulses at a second wavelength, different from thefirst wavelength, wherein the second wavelength is at an excitationwavelength of the first cellular activity-dependent fluorescent moiety;and a fourth set of light pulses at a third wavelength, different fromthe first and second wavelengths, wherein the third wavelength is at anexcitation wavelength of the second cellular activity-dependentfluorescent moiety, and wherein the recording comprises recording afirst image and a second image of the terminal cross-section of themultimode optical fiber from the region, wherein a cross-sectionalaverage of the fluorescence generated in response to the third set oflight pulses in the first image is representative of an aggregate neuralactivity of the first collection of a plurality of neurons, and across-sectional average of the fluorescence generated in response to thefourth set of light pulses in the second image is representative of anaggregate neural activity of the second collection of a plurality ofneurons.
 5. The method according to claim 1, wherein the firstwavelength is at an isosbestic point of at least one of the one or morecellular activity-dependent fluorescent moieties.
 6. The methodaccording to claim 1, wherein the analyzing comprises 4) subtracting anaverage of the cellular activity-independent fluorescence across across-section from an average of the cellular activity-dependentfluorescence across the cross-section, to obtain a motion-correctedmeasure of the aggregate cellular activity.
 7. The method according toclaim 1, wherein the one or more cellular activity-dependent fluorescentmoieties comprise a calcium- and/or a voltage-sensitive indicator dye.8. The method according to claim 1, wherein the image detector is acharge-coupled device (CCD) or a complementary metal oxide semiconductor(CMOS) camera.
 9. The method according to claim 1, wherein thefluorescence emitted from the region is split using an image splitter toform and record a separate image for the fluorescence emitted by each ofthe one or more cellular activity-dependent fluorescent moieties. 10.The method according to claim 1, wherein the plurality of wavelengthscomprise wavelengths of 440 nm to 620 nm.
 11. The method according toclaim 2, wherein the multimode optical fiber has a diameter of 400 μm.12. The method according to claim 5, wherein the isosbestic point isbetween 405 nm to 420 nm.
 13. The method according to claim 1, whereinlight pulses in the first set are pulsed at a first frequency less thana second frequency at which light pulses of the second set are pulsed.14. A system comprising: a) an illumination unit; b) an objective,wherein the objective is configured to receive light from theillumination unit and to focus the light at a working distance from theobjective; c) a plurality of light conduits, each light conduitcomprising one or more multimode optical fibers and defining a firstend, a second end opposite the first, and a light conduit numericalaperture, wherein a terminus at the first end of each of the lightconduits is at the working distance from the objective; a terminalcross-section corresponding to each of the one or more multimode opticalfibers at the first end of each of the light conduits is in a field ofview of the objective; and the light conduit numerical aperture is lessthan a numerical aperture of the objective; d) an image detector; e) aprocessor; and f) a computer-readable medium comprising instructionsthat, when executed by the processor, causes the system to: generate alight stimulus comprising i) a first set of light pulses at a firstwavelength; and ii) a second set of light pulses at one or morewavelengths, each of the one or more wavelengths different from thefirst wavelength and wherein each light pulse of the first set areinterleaved among light pulses of the second set, using the illuminationunit, to illuminate a plurality of regions in a target tissue, eachregion at the second end of each of the plurality of light conduits,wherein the regions are labeled with one or more cellularactivity-dependent fluorescent moieties, wherein the plurality ofwavelengths comprises one or more wavelengths at an excitationwavelength of the one or more cellular activity-dependent fluorescentmoieties, thereby generating fluorescence from each region; collect thegenerated fluorescence from each region via the second end of the samelight conduit of the plurality of light conduits used to illuminate theregion, where the collected fluorescence is transmitted through each ofthe plurality of light conduits to each corresponding first end; recordan image including each of the one or more terminal cross-sections atthe first ends of all of the plurality of light conduits using the imagedetector; and analyze the recorded image, to generate an outputcomprising a measure of aggregate cellular activity in the regions,wherein the analyzing comprises: 1) demarcating the terminalcross-sections in the recorded image; 2) calculating an average of thefluorescence across the terminal cross-sections; and 3) calculating anormalized change in the fluorescence over a baseline fluorescence theterminal cross-sections in the recorded image, wherein the baselinefluorescence is a median of the average fluorescence within the terminalcross-sections across a plurality of recorded images.
 15. The system ofclaim 14, wherein the one or more multimode optical fibers have adiameter in the range of 100 to 1000 μm and the image detector comprisesan image sensor.
 16. The system of claim 14, wherein each of the lightconduits comprises: an implantable fiber-optic element comprising anattachment element; and the one or more multimode optical fibers areconfigured to attach to the attachment element.
 17. The system of claim14, wherein the plurality of wavelengths comprises a wavelength at anisosbestic point of the one or more cellular activity-dependentfluorescent moieties.
 18. The system of claim 14, wherein the pluralityof wavelengths comprises a plurality of wavelengths at an excitationwavelength of a plurality of cellular activity-dependent fluorescentmoieties.
 19. The system of claim 14, wherein the plurality ofwavelengths comprises one or more wavelengths at an activationwavelength of one or more light-activated polypeptides.
 20. The systemof claim 14, wherein the illumination unit is a light-emitting diode(LED) or an LED array or a laser.
 21. The system of claim 14, whereinthe image detector is a charge-coupled device (CCD) or a complementarymetal oxide semiconductor (CMOS) camera.
 22. The system of claim 14,further comprising an image splitter.
 23. The system of claim 14,wherein the regions comprise one or more collections of a plurality ofneurons, or a subcellular portion thereof, and the one or morecollections of a plurality of neurons comprise one or morefunctionally-defined collections of a plurality of neurons; wherein theone or more cellular activity-dependent fluorescent moieties are one ormore neural activity-dependent fluorescent moieties.
 24. The system ofclaim 14, wherein the objective is a microscope objective.
 25. Thesystem of claim 14, wherein the plurality of wavelengths comprisewavelengths of 440 nm to 620 nm.
 26. The system of claim 17, wherein theisosbestic point is between 405 nm to 420 nm.
 27. The system of claim22, wherein the image splitter is configured to: split the fluorescenceemitted from each region to separate the fluorescence emitted by each ofthe one or more cellular activity-dependent fluorescent moieties;collect the separated fluorescence from each region via the second endof the same light conduit of the plurality of light conduits used toilluminate the region; and record a separate image for the fluorescenceemitted by each of the one or more cellular activity-dependentfluorescent moieties, including each of the one or more terminalcross-sections at the first ends of all of the plurality of lightconduits, using the image detector.